The price quoted in your first vendor meeting has almost no relation to what you’ll actually pay. In a survey of 200 IT directors across Europe, the average ERP project budget overrun was 47% compared to initial estimates. Here’s how to build a realistic budget.
What you’ll find in this article:
- Complete TCO (Total Cost of Ownership) structure over 5 years
- Hidden costs that vendors never mention upfront
- Realistic budget ranges by company size
- Four rules to secure your budget envelope
Why are initial quotes systematically underestimated?
There’s no systematic bad faith from vendors or system integrators. The causes are structural — understanding them helps you ask the right questions from the first commercial meetings:
From the vendor side: salespeople propose a minimum scope to secure the purchase order, knowing that customization requests will come later.
From the client side: requirements are poorly formalized upfront. “Forgotten” processes during initial quoting often represent 20-30% of the final scope.
From the integrator side: workload estimates are based on “typical” projects that never exactly match your context.
Total Cost of Ownership (TCO) structure over 5 years
1. Licenses or SaaS subscriptions (25–35% of TCO)
For on-premise ERP (installed on your servers), licenses are purchased once then subject to annual maintenance of 15-22% of the initial price.
For SaaS ERP (cloud-hosted), you pay a monthly subscription per user. Beware: user count tends to grow, and add-on modules are billed separately.
Frequent hidden cost: “named” vs “concurrent” licenses. A named license is assigned to a specific user. A concurrent license allows N simultaneous connections. For a team of 100 people using ERP part-time, 25 concurrent licenses might suffice — but vendors rarely suggest this spontaneously.
2. Integration and deployment (30–40% of TCO)
This is the most variable and hardest-to-estimate cost item. It includes:
- Business requirements analysis and functional specifications
- ERP configuration (setup without development)
- Data migration (historical data transfer)
- Custom development (interfaces with other systems, bespoke modules)
- Testing (functional acceptance, load testing)
- Deployment and go-live
Rule of thumb: for a project with £150K in licenses, budget between £200K and £400K for integration services.
3. Data migration (often ignored, 5–15% of TCO)
Data migration is systematically underestimated. Common problems:
- Source data quality: duplicates, inconsistencies, missing data in the old system
- Volume: migrating 10 years of transaction history can require weeks of work
- Mapping: your old system’s data model and the new ERP never match perfectly
Tip: plan for 3-5 dry-run migrations before go-live. Each cycle reveals new data quality issues.
4. Infrastructure (for on-premise solutions)
If you choose an internally hosted ERP, add:
- Production and pre-production servers
- Backups and disaster recovery plan
- Security and VPN access for remote users
- System administration costs
For SaaS ERP, these costs are included in the subscription — but ensure your internet bandwidth is sufficient.
5. Training (5–10% of TCO, often cut first)
Training is the first item reduced when facing budget overruns. This is a strategic mistake.
Distinguish between:
- Project team training (key users): people who know the ERP inside out and will train others
- End-user training: tailored to each profile (accountant, purchaser, salesperson, etc.)
- Administrator training: to manage the ERP autonomously after go-live
Budget 3-5 training days per user profile for a medium-sized ERP.
6. Change management (often neglected, 10–15% of TCO)
Studies show that 70% of ERP failures are human-related, not technical. A change management budget covers:
- A dedicated internal communication manager
- Co-creation workshops with future users
- Regular information sessions for management
- Enhanced support during the first 3 months post go-live
For more on this topic, check our practical ERP change management guide.
7. Maintenance and evolution (15–25% of TCO annually)
After go-live, costs don’t stop:
- Application maintenance: bug fixes, regulatory updates (VAT, payroll, etc.)
- Functional evolution: new processes, new integrations, new modules
- Major updates: ERPs release major versions every 2-4 years. Version migration often costs 20-40% of initial deployment cost.
Budget model for mid-market ERP project (200 users, Tier 2 ERP)
| Item | Low budget | High budget |
|---|---|---|
| Licenses / SaaS 5 years | £250K | £400K |
| Integration and deployment | £300K | £600K |
| Data migration | £50K | £120K |
| Training | £40K | £80K |
| Change management | £40K | £100K |
| Infrastructure (if on-premise) | £50K | £150K |
| 5-year maintenance (excl. licenses) | £100K | £200K |
| Total 5-year TCO | £830K | £1,650K |
The range is wide because it heavily depends on the level of customization chosen and your starting data quality. A project with minimal customizations and clean data approaches the lower bound. A heavily customized project with heterogeneous data approaches — or exceeds — the upper bound.
How to secure your budget
1. Request a data audit before the migration quote. A good integrator will propose upstream data quality analysis.
2. Negotiate a capped fixed-price, not a time-and-materials agreement. A T&M project (billing at actual man-days) is a blank check.
3. Build a 20% contingency reserve for unforeseen issues. Not to spend systematically, but to avoid sabotaging training or change management at project end.
4. Contractualize payment milestones on specific deliverables, not dates. You pay when user acceptance testing is validated, not when the integrator declares being “ahead of schedule”.
Most frequent hidden costs by ERP type
SaaS ERP: pricing traps to watch
Annual subscription increases. Most SaaS contracts include an inflation indexation clause (CPI) or capped increases at 5-8% per year. Over 5 years, 5% annual increases represent +28% on your initial license budget. Negotiate at signing.
Uncapped usage-based billing. Some vendors bill per transaction (invoices issued, orders processed). If your business grows 30%, your subscription can rise mechanically without adding a single user.
“Optional” modules becoming essential. SaaS ERP modular pricing is designed for you to start with a low base and add modules over time. List exhaustively what modules you’ll need in 3 years and ask for full pricing upfront.
Bandwidth costs. SaaS ERP consumes 2-10 times more bandwidth than on-premise ERP. If your network infrastructure isn’t sized properly, you’ll need to invest in connectivity — a cost often forgotten in budgets.
On-premise ERP: underestimated infrastructure costs
Hardware renewal. ERP servers have a 5-7 year lifespan. On a 10-year TCO, plan at least one complete hardware renewal cycle.
Major version updates. SAP, Oracle and other major vendors impose regular updates with significant implementation costs. SAP S/4HANA requires migration from SAP ECC that often costs 30-60% of the initial project. These costs are rarely integrated in vendor TCO projections.
Redundancy and high availability. If your ERP must be available 24/7, you need redundant architecture (clustering, automatic failover). Double your infrastructure budget for true high availability.
Budgets by company size: real ranges
SME (10–50 users) — Tier 3 ERP (Odoo, Sage, NetSuite Starter)
| Item | Realistic budget |
|---|---|
| Licenses / SaaS 5 years | £15,000 – £50,000 |
| Integration and deployment | £20,000 – £60,000 |
| Data migration | £5,000 – £20,000 |
| Training | £5,000 – £15,000 |
| Change management | £5,000 – £15,000 |
| Total 5-year TCO | £50,000 – £160,000 |
Mid-market (50–200 users) — Tier 2 ERP (Dynamics 365, NetSuite)
| Item | Realistic budget |
|---|---|
| Licenses / SaaS 5 years | £150,000 – £350,000 |
| Integration and deployment | £200,000 – £450,000 |
| Data migration | £30,000 – £80,000 |
| Training | £25,000 – £60,000 |
| Change management | £30,000 – £80,000 |
| Infrastructure (if on-premise) | £40,000 – £120,000 |
| Total 5-year TCO | £475,000 – £1,140,000 |
Enterprise (200–1000 users) — Tier 1 ERP (SAP S/4HANA, Oracle)
At this level, ranges become very wide (£2M to £15M+) depending on process complexity and module count. An article won’t help — you need an independent consulting firm to build the TCO.
The cost of inaction: what nobody calculates
Before focusing on project cost, calculate the cost of doing nothing:
- How many FTE (full-time equivalents) are dedicated to manual tasks that ERP would automate?
- What’s the cost of data entry errors, duplicates, and manual reconciliation?
- How much does the inability to have real-time consolidated business visibility cost?
- What business opportunities do you miss due to an inadequate information system?
In most cases, ROI for a well-implemented ERP is positive in 3-5 years. But you need to calculate it explicitly to justify the investment internally and convince reluctant stakeholders.
Key takeaway: An ERP project isn’t an IT expense. It’s an investment in operational capacity and company competitiveness. Present it as such to your board of directors.
