How Much Does an AI Chatbot Cost in the UK?
A grounded AI chatbot over your existing documentation typically costs £10,000–£30,000 to build in the UK, plus running costs per conversation. An agent that takes actions in your systems costs more — usually £30,000+ — because permissions, confirmation flows and audit logging are most of the work.
The reason quotes vary so widely is that “chatbot” covers three different products. A scripted decision-tree bot, a grounded assistant answering from your content, and an agent that actually does things are separated by an order of magnitude in both cost and risk.
Build cost by type
| Type | Typical build | What it does |
|---|---|---|
| Scripted bot | £2,000 – £8,000 | Decision tree, no model. Predictable, limited |
| Grounded assistant | £10,000 – £30,000 | Answers from your documents with citations |
| Agent | £30,000+ | Takes actions in systems, with permissions and audit |
| Off-the-shelf SaaS | £50 – £500/month | Fast, limited control, your data on their terms |
The running costs people forget
- Model usage, charged per token. Trivial at low volume, significant at high volume — model it at realistic traffic before committing.
- Vector storage for retrieval, which is modest but not nothing.
- Content maintenance. An assistant grounded in documentation that nobody updates gets worse every month.
- Evaluation. Re-running your test set when you change a prompt or a model version.
- Escalation handling. Someone has to pick up what the assistant cannot answer.
Working out whether it pays
The honest calculation is narrower than most business cases suggest. Take the volume of enquiries that are genuinely repetitive and answerable from existing documentation — not your total enquiry volume. Assume the assistant handles a share of those, not all. Compare the time saved against build plus running cost over two years. If the sums only work at optimistic deflection rates, the project is marginal and worth deferring.
Frequently asked questions
Is a custom build better than an off-the-shelf tool?
Not automatically. SaaS chatbots are good and improving, and for standard support use they are frequently the right call. Custom earns its cost when you need the assistant grounded in systems the SaaS cannot reach, or when the data cannot leave your environment.
What ongoing cost should we budget?
Model usage plus maintenance. The maintenance half is the one that surprises people: documentation drifts, questions change, and an assistant left alone for a year will be confidently answering from material that is no longer accurate.
Can it handle sales enquiries as well as support?
Technically yes, and it is worth being cautious. Support questions have correct answers in your documentation. Sales conversations involve commitments, pricing judgement and qualification — exactly where a confident wrong answer costs most. Capture and route rather than letting it negotiate.
How long does it take to build?
A grounded assistant is typically six to ten weeks including the evaluation set. Agents take longer, because most of the work is the permissions, confirmations and audit trail rather than the conversation.
We build these as AI agent and chatbot projects, with an evaluation set from the start so you can tell whether it is working.
