What a side project actually costs to run
Real monthly bills from solo builders, and the three line items that turn a £0 project into a £40 one without you noticing.
Almost every stack marketed at solo builders has a free tier that covers a project doing nothing. The interesting question is what happens when something works.
Here's where the money actually appears.
The genuinely free part
For a site with a few thousand visitors a month, this costs nothing and will keep costing nothing:
- Hosting on Vercel's hobby plan or Cloudflare Workers
- Postgres on Supabase or Neon's free tier
- Transactional email on Resend (3,000 a month free)
- A repo on GitHub
The only guaranteed bill is your domain. Call it £12 a year for a .co.uk, £30 for a .dev or a .com.
So the honest answer for most projects is about £2 a month.
Where it stops being free
Three things, in the order they usually bite.
Supabase pausing your database. The free tier pauses a project after a week with no activity. Fine while you're building. Less fine when someone finds your site three weeks after you stopped touching it and gets an error. That's $25 a month to avoid, and it's the most common first bill I see on submissions here.
Email volume. Resend's free tier is 3,000 a month, which sounds like plenty until you add a weekly digest. 500 subscribers times 4 weeks is 2,000 emails before you've sent a single password reset. Next tier is $20.
Vercel's hobby limits. The one that catches people isn't bandwidth, it's the commercial-use rule. Once your side project takes money, you're supposed to be on the $20 Pro plan. Plenty of people ignore this until they get an email about it.
Add those three up and a project with a few hundred users lands around £50 a month.
The one that surprises everyone
Anything with an AI feature in it.
A wrapper doing a few hundred generations a day will run somewhere between £15 and £150 a month depending on the model and how long your prompts are. It's the only line item on this list that scales directly with how popular you get, which means a post that does well on Hacker News can cost you real money in a single afternoon.
Put a hard spending cap on the API key. Do it on day one, not after the bill.
Keeping it near zero
A few things that genuinely work:
Static-render everything you can. A directory or content site has no reason to hit a database on every request. Cache for an hour and your database usage drops to almost nothing.
Put Cloudflare in front of it. Free, and it absorbs the traffic spike that would otherwise show up on a metered bill.
Use one platform's free tier properly rather than four. Every service you add is another thing with its own limits, its own billing surprise, and its own 2am email.
Set billing alerts on everything the day you sign up. The worst version of this story always starts with someone finding out a month later.
The number on each build page
Every project listed here has a running cost on its page, self-reported by the person who built it. The range is wide, the median is low, and the outliers are almost always AI features or somebody who moved to a paid database tier and never looked at it again.