The Hidden Costs of Hiring a UK Agency to Build Your SaaS
You’ve had the idea. You’ve validated it. You’ve spoken to a handful of UK digital agencies and you’re sitting on a stack of proposals ranging from £40,000 to £200,000+. Before you sign anything, there are costs buried deep in those contracts that most agencies will never volunteer upfront — and they could double what you end up spending before your platform ever sees a single paying customer.
This post is written by By Design UK, a SaaS and Shopify development studio based in EN3 7LW. We’ve built production-ready SaaS platforms from £18,000, including Tackly.co.uk — a live platform now serving 25 industries across the UK. We know exactly what agencies charge, why they charge it, and what founders often don’t find out until it’s too late.
What Does a UK Agency Actually Charge to Build a SaaS?
Let’s start with the headline numbers. A mid-tier UK digital agency will typically quote:
- Discovery & scoping phase: £3,000 – £8,000 (charged before a line of code is written)
- MVP build: £45,000 – £120,000 depending on complexity
- Design (UX/UI): Often billed separately — £8,000 – £25,000
- QA and testing: £5,000 – £15,000, frequently added late in the project
- Project management fee: 15–20% added on top of the total build cost
That “£50,000 MVP” can rapidly become £80,000 – £100,000 once every line item is added. And that’s before we get to the costs most founders never anticipate.
What Are the Hidden Costs Nobody Warns You About?
Is the Discovery Phase Really Necessary — or Is It Just Billable Hours?
Many large agencies insist on a paid discovery phase before committing to a full project quote. On paper, this sounds sensible. In practice, you’re often paying £3,000 – £8,000 for a scoping document and a set of wireframes that any experienced developer could produce as part of a standard brief. Some agencies use discovery phases as a way to lock you in early and increase the eventual build estimate once they have full visibility of the project.
At By Design UK, we provide detailed project scoping as part of your initial consultation — at no additional cost. You can get in touch with our team here to start that conversation.
Will You Own Your Code When the Project Ends?
This is one of the most overlooked contract clauses in UK agency agreements. Some agencies retain intellectual property rights to the codebase until the final invoice is paid in full. Others build on proprietary internal frameworks, meaning you can’t take the code elsewhere without starting from scratch. If you ever want to switch developers or bring development in-house, you could be looking at a rebuild costing £20,000 – £60,000.
Always insist on full IP transfer upon project completion and ensure the platform is built on open, documented technology — not a black-box internal system.
What Happens When You Need Changes After Launch?
Agencies typically offer a post-launch support retainer at £1,500 – £5,000 per month. Outside of that retainer, even a simple feature change — the kind that takes a competent developer four hours — can be quoted at a fixed project rate of £800 – £2,500. This is where early-stage SaaS founders bleed money the fastest. Your product will need to iterate rapidly after launch. If every change requires a new purchase order and a two-week turnaround, your competitive advantage disappears.
Are Infrastructure and Third-Party Costs Included in the Quote?
Almost never. Agencies build and hand over. They typically don’t include:
- Cloud hosting setup (AWS, Google Cloud, Azure): £200 – £1,500/month ongoing
- Payment gateway integration (Stripe, GoCardless): Setup fees of £500 – £2,000 depending on complexity
- Email delivery infrastructure (SendGrid, Mailgun): £50 – £300/month
- SSL, domain, DNS configuration: Small but often forgotten until go-live
- GDPR compliance audit: £1,000 – £4,000 if conducted by a third party
A realistic total cost of ownership for a SaaS platform in its first year — including agency build fees, ongoing hosting, third-party tools, and change requests — can easily reach £80,000 – £180,000 when built through a traditional large agency model.
Why Do So Many Founders Overpay for SaaS Development?
The answer is a combination of inexperience, urgency, and the weight of a polished agency pitch deck. Large agencies are exceptionally good at selling. They have case study libraries, slick proposals, and dedicated sales teams. What they don’t always have is the lean, direct relationship that actually gets an early-stage SaaS product built efficiently.
Founders often conflate agency size with quality. In reality, your project will likely be handed to a mid-level developer two weeks after contracts are signed, while the senior team who sold you the project moves on to the next pitch.
Is There a More Cost-Effective Route to Building a UK SaaS?
Yes — and it doesn’t mean compromising on quality or going offshore. Boutique UK development studios like By Design UK operate with lower overheads, direct founder-to-developer communication, and a genuine interest in the long-term success of the platforms they build.
Our SaaS development service starts from £18,000 — and that’s for a production-ready platform with real users, not a prototype. Tackly.co.uk is live proof of what we deliver: a fully operational SaaS platform currently serving 25 industries across the UK, built with scalability and clean architecture from day one.
We also build Shopify stores from £499 for businesses that need a fast, professional eCommerce presence without agency-level overhead.
If you’re comparing proposals and want a straight-talking conversation about what your SaaS actually needs — and what it should actually cost — use our contact page to reach us directly.
What Should You Ask Before Hiring Any UK Agency?
Before signing any agreement, get clear answers to these questions:
- Who specifically will be building my platform day-to-day?
- Do I own 100% of the IP and code on completion?
- What technology stack will you use, and why?
- What are your rates for post-launch change requests?
- Can I see a live example of a SaaS platform you’ve built?
- What isn’t included in this quote?
If an agency hesitates on any of these — particularly the last one — treat that as a red flag.
Ready to Build Your SaaS Without the Hidden Costs?
By Design UK is a UK-based development studio operating from EN3 7LW. We build SaaS platforms from £18,000 and Shopify stores from £499, with full transparency on costs, clear IP ownership, and a direct working relationship from brief to launch.
You can see our work live at Tackly.co.uk — a real SaaS platform serving real businesses across 25 industries.
To discuss your SaaS project, submit an enquiry via our contact page or call us directly on 020 3951 4908. No discovery fee. No sales deck. Just a direct conversation about what you’re building and how we can help.