The Real Cost of SaaS Customisation: When You Are Already Building Custom Software

There's a moment in many companies' lifecycles when they realise their "SaaS subscription" actually involves $80k/year of custom development consulting on top of $40k/year of licensing — and they think this is somehow different from building custom software. It isn't. It's custom software, built on someone else's platform, paid for at premium rates, with all the downsides of vendor lock-in.

Here's the honest math.

The pattern

It usually goes like this:

Year 1: Adopt Salesforce / HubSpot / NetSuite. Standard pricing, light customisation.

Year 2: First custom field, first custom workflow, first custom report. Maybe $5k/year in consulting fees.

Year 3: Workflow gets more complex. Three or four custom apps built on the platform. $20k/year in consulting.

Year 4: Custom Apex / Lightning / SuiteScript. $50k/year in consulting.

Year 5: You realise you have a custom application that happens to live inside Salesforce. $80–120k/year in licensing + consulting combined.

What you've actually built

By year 5, you've built custom software. The reality:

60–80% of the functionality is in custom code you (or your consultants) wrote

20–40% is core SaaS functionality you genuinely use

100% is locked inside the SaaS vendor's platform

If you exported the system today, you'd have nothing portable. The custom code requires the vendor's platform. The data is in their schema. The workflows assume their UI.

The cost comparison

Year 5 of heavy SaaS customisation vs year 5 of native custom build:

Heavy SaaS customisation path

Year 5 SaaS licensing: $80–150k/year

Year 5 customisation consulting: $40–100k/year

5-year cumulative: $400k–1M+

Ownership: zero

Exit story: rebuild from scratch

Native custom build path

Year 1 build: $80–180k one-time

Year 2–5 maintenance: $30–60k/year × 4 = $120–240k

5-year cumulative: $200–420k

Ownership: complete

Exit story: continue running, no vendor

Why this happens

Three reasons companies end up in heavy SaaS customisation rather than native custom:

Sunk cost. "We've already paid for Salesforce licensing, might as well build on top."

Procurement friction. Adding a custom dev contract is hard. Adding more SaaS consulting hours is easy (existing vendor).

Optical preference. "We use Salesforce" sounds better to investors than "we built custom software."

None of these are good reasons. The math favours native custom by year 3–4 in almost every case.

When SaaS customisation is genuinely OK

Light customisation (5–10% of standard SaaS work) on top of a 60–80% standard SaaS usage pattern — totally fine. Add a couple custom fields, write a few Zapier flows, build one or two simple apps.

The line gets crossed when:

Customisation consulting exceeds 50% of licensing fees

You have a dedicated "Salesforce developer" or equivalent

You've built more than 3–4 substantial custom apps on the platform

The custom code is no longer documented because the consultant turned over

The replatform decision

Once you're in heavy customisation territory, the question becomes "when to replatform to native custom."

The replatform decision is easier when:

Annual SaaS+consulting exceeds $150k/year

The custom code is documented and the team understands it

The business is stable enough to invest in a 6–12 month migration

Vendor pricing or strategy has changed materially against your interests

If you're considering this move, see our NetSuite migration playbook — the principles apply to migrating off any heavily-customised SaaS.

For a transparent cost comparison for your specific scope, our cost calculator runs 5 questions. Or contact us for a 48-hour scope.