The short answer
Plan on A$60,000 to A$250,000 plus GST to rebuild a typical mid-market business system on a modern stack.
Our pricing starts with a two-week assessment at A$9,500 to A$15,000 plus GST, then fixed-price phases of A$25,000 to A$80,000 plus GST each. Most systems need two to four phases. Core banking, mainframe and whole-of-government platforms are a different category and cost many times more.
I get asked some version of this question every month, usually by a CFO or COO with an Access database, a VB6 app or an old .NET system quietly running a core part of the business. They have just received a quote that looks like a phone number. The price depends on a handful of things you can mostly find out in two weeks. Here is what they are.
What drives the cost
The size and shape of the system
Line counts are a poor guide. What matters is how many business functions the system performs, how many screens and reports people actually use, and how much logic is buried in the code. Forty screens that mostly show and edit records cost less to rebuild than ten screens that each run complex pricing or scheduling rules.
Integrations
Every connection adds cost: the accounting package, the CRM, a supplier portal, a nightly file drop to the bank. Old systems often connect through shared folders, direct database links or manual exports, and each one has to become a proper integration. This is where most underquoted projects come unstuck.
Data migration
Twenty years of data is rarely clean. Expect duplicate customers, free-text fields used for three different things, and records that only make sense if you know a workaround someone invented in 2011. Cleaning, mapping and reconciling it is real work, and it has to be rehearsed before go-live.
Compliance and security
If the system holds personal, health or financial information, the new one needs access control, audit logging and hosting that meets the Privacy Act and any industry rules. The old system probably never had these, so they add scope.
Retire, replace, refactor or rebuild
Before you compare quotes, make sure you are comparing the right options. These are the four I cost in every assessment.
| Option | Upfront cost | Best when | Watch out for |
|---|---|---|---|
| Retire | Lowest | Another tool already does most of what the system does | Hidden users and reports nobody told you about |
| Replace with SaaS | Low to medium, then ongoing fees | A mainstream product covers almost everything you need | Customisation costs, and changing your process to fit the product |
| Refactor | Medium | The platform is still supported and the structure is sound | Paying to modernise code you would have replaced anyway |
| Rebuild | Medium to high | The platform is out of support and the system encodes how your business works | Big-bang rewrites that take 18 months before anything ships |
Compare the options over five years, not just upfront. A SaaS product at A$40 per user per month looks cheap until you multiply it by 150 users and 60 months and add the integration work. A rebuild looks expensive until you take away the licence fees and the cost of the workarounds you run today.
Why AI has changed the maths
Most of the cost in a legacy rebuild used to go on understanding the old system: reading undocumented code, working out business rules and writing tests to prove the new system behaves the same way. AI coding tools now do much of that first pass quickly. McKinsey reported that gen AI can deliver 40 to 50 percent faster modernisation timelines and around 40 percent lower costs from technology debt.
You still cannot point an AI at old code and get a new system. The tools miss context and make confident mistakes. The saving only holds when an experienced engineer checks every rule the AI extracts against how people really use the system.
That is why one of our CTOs leads every rebuild. The CTO reviews the system, plans the phases and runs delivery, and a small team of AI-driven developers does the build under that review.
Red flags in a modernisation quote
If a quote shows any of these, ask hard questions before you sign.
A fixed price with no discovery
Nobody can price a rebuild accurately without understanding the old system first. Either the quote is padded or variations are coming.
One big go-live date
Big-bang cutovers fail more often and give you nothing usable until the end. Ask for phased delivery with working software every few weeks.
No line for data migration
If the quote does not mention data cleansing, mapping and rehearsal, it is not in the price.
A proprietary platform
If you cannot take the code and host it yourself, you have swapped one dependency for another.
No mention of buying instead
A vendor who only sells builds will rarely tell you that a SaaS product would do the job.
How to get a reliable number
Pay for a short, fixed-price assessment before you commit to anything larger. It should give you a written map of what the system does, a catalogue of its business rules, costed options (including the ones that do not involve the vendor) and a fixed price for each phase. Even if you decide not to rebuild, that catalogue of business rules is valuable when you choose a SaaS product.
Keeping what works matters as much as rebuilding what does not. In our ERP migration rescue for a Victorian manufacturer, about 60% of the existing configuration was sound. Rebuilding only the broken integration layer and data migration recovered roughly A$240k of a stalled A$400k investment.
If you are dealing with an Access database, our guide to moving an Access database to a web app covers that path in detail.
Step 1 · 2 weeks
Modernisation Assessment
A$9.5k to A$15k + GST, fixed
System map, business rules catalogue, costed options and a fixed price per phase.
Step 2 · per phase
Rebuild phases
A$25k to A$80k + GST each
Working software at the end of each phase. Most systems need two to four.
Common questions
How much does legacy system modernisation cost in Australia?
For a mid-market business system, our two-week assessment costs A$9,500 to A$15,000 plus GST. Each rebuild phase is fixed at A$25,000 to A$80,000 plus GST, and most systems need two to four phases, so a typical total is A$60,000 to A$250,000 plus GST. Large core platforms such as banking or mainframe systems cost far more and need a large systems integrator.
Is it cheaper to rebuild a legacy system or replace it with SaaS?
SaaS is usually cheaper up front when a mainstream product covers almost everything the system does. Rebuilding is often cheaper over five years when the system encodes processes that set your business apart, or when SaaS would need expensive customisation and workarounds. Cost both options over five years, including subscription fees, integration and data migration, before deciding.
Why do legacy modernisation quotes vary so much?
Most of the cost sits in understanding what the old system really does, migrating its data and testing that nothing was lost. Vendors who skip that discovery work either pad the quote heavily to cover the unknowns or quote low and raise variations later. A fixed-price assessment first removes most of the guesswork.
