The verdict in three sentences
Rebuilding a legacy application (Access, VB6, Delphi, old PHP) into a modern SaaS costs, in 2026, between EUR 80,000 and EUR 200,000 depending on system size and data volume. The number-one risk is not technical, it is the big bang: rewriting everything at once and freezing the business. The right method is a progressive migration (strangler pattern), which replaces the old system module by module without interruption.
The items of a legacy rebuild
A successful rebuild always starts by understanding the existing system before writing a single line of new code.
| Phase | Goal | Estimated effort |
|---|---|---|
| Audit & mapping | Understand the legacy, hidden business rules | 10-20 days |
| Target architecture | Define the cloud stack and modules | 8-15 days |
| Progressive migration | Replace module by module | 60-120 days |
| Data migration | Clean, map, transfer | 15-30 days |
| Testing & acceptance | Verify functional parity | 15-25 days |
| Cutover & training | Go live, train | 8-15 days |
Detailed budget (2026 estimate)
Day rate for a rebuild team in Dublin in 2026: EUR 450-650.
| Item | Cost EUR |
|---|---|
| Audit & mapping | 6,000-13,000 |
| Target cloud architecture | 5,000-10,000 |
| Development (strangler) | 40,000-110,000 |
| Data migration | 9,000-22,000 |
| Testing & acceptance | 9,000-18,000 |
| Cutover, training, docs | 5,000-12,000 |
| Rebuild total | 80,000-200,000 |
The return on investment
Legacy is expensive in silence: outages, manual entry, a single developer who holds all the knowledge. Modernization cuts these hidden costs.
| Indicator | Before (legacy) | After (modern SaaS) |
|---|---|---|
| Annual maintenance cost | EUR 45,000 | EUR 22,000 (-51%) |
| Blocking incidents / month | 6-10 | 1-2 |
| Time to add a feature | 4-8 weeks | 3-7 days |
| Mobile / remote access | No | Yes |
| Data loss risk | High | Low (auto backup) |
| Single-person dependency | Critical | None |
Mini case study
Marc, IT director of an industrial mid-cap in Dublin (120 employees), runs a 2009 Access application on which all production management depends. A single external provider maintains it at EUR 45,000/year, and each crash halts the workshop. He invests EUR 145,000 in a strangler-pattern SaaS rebuild over 8 months. Maintenance drops to EUR 22,000/year (EUR 23,000 saved), incidents fall from 8 to 1 per month, and production gains mobile access. Full ROI is reached in about 3.5 years, not counting the end of single-person dependency risk.
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FAQ
Why not rewrite everything at once?
Big bang is the leading cause of rebuild failure: slipping deadlines, the old system frozen for 10 months, a risky cutover. The strangler pattern delivers value from the first months and removes the tunnel effect.
Can we keep historical data?
Yes. Data migration is part of the project: we clean, map, and transfer history into the new database, with consistency checks at every step.
What does maintenance cost after the rebuild?
As a 2026 order of magnitude, expect support of 15 to 25% of the build cost per year, i.e. typically EUR 20,000 to 40,000/year, often half the cost of maintaining a fragile legacy system.
How long does a rebuild take?
Between 6 and 10 months for a medium-sized system, with modules delivered and used in production well before the project ends.
What happens to the old application during the rebuild?
It keeps running. The strangler pattern lets old and new coexist, and removes the old module only once the new one is validated.
Let's scope your project. Send us your legacy application type, user count, and data volume: we frame a progressive rebuild plan priced between EUR 80,000 and EUR 200,000. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
