I run a small web studio in the UK and I get asked this constantly, so here is the itemised version rather than a number pulled out of the air.
Hosting on an edge platform: £0 to £4. A small business site genuinely sits inside a free tier most months.
Domain, amortised: about £0.80. A .co.uk is roughly £10 a year.
SSL certificate: £0. It has been free since Let's Encrypt.
Email routing: £0 to £6, depending on whether you want a real mailbox or just forwarding.
Backups and monitoring: £0 to £2.
Maintenance labour: £25 to £40. This is the only line that is genuinely expensive, and it is the one nobody itemises.
The floor is roughly £26 to £53 a month before anyone makes a penny. So if you are quoted £15 a month, either you are being subsidised into a lock-in or nobody is maintaining anything. If you are quoted £300, ask what the labour line is actually buying.
Two things worth insisting on whoever builds it: the domain is registered in your own name, and it says in writing that the code and the content are yours if you leave.
Source: r/u/hibbaco · by /u/hibbaco