FTR Ive been running a HP Pro Slimline (cost 30 euros second hand from marktplaats) with 8 gb ram and 500 gb disk for 2 years out of my house. The machine is probably 5 - 10 years old at a guess. I upgraded from 4gb ram to 8gb after one year for a blistering 20 euros.
The server hosts a software called foodsoft and powers the ordering system of a local food co-operative (https://biobulkbende.org) which currently has around 80 members (including myself) ordering between 800 - 2000 euros worth of dry goods and local veggies (within 15 km of Rotterdam) every month since around 2 years.
I do 1 to 2 hours of routine server and app maintenance every odd month. We have a working group for taking care of stuff at the food co-op. Ive not noticed any issues with my home connection (e.g. slowness). I don't notice any extraordinary costs on my energy bill.
Members like that their data is literally around the corner and they can just call us up if something weird happens. I even invited people over to see the server.
I think this machine could probably support a couple of hundred more folks from the neighbourhood.
We don't need data centers or IT companies or technical "experts"!