If you squeeze it you could probably get down to 3-400 euros per year starting from the second year (due to one-time fees the first year) if you do your own books and taxes and whatnot, but just paying upfront for keeping things neat according to the local bureaucracy is likely a kind of convenience you'd want.

I'd say you should start buying some services from european infra and compute providers and see if your ideas make money. You can get away with very little if you get some storage and processing time through e.g. Scaleway or Hetzner, and with a bit of fiddling I expect them to sell to you regardless of whether you have a company or not. If you start making money enter some Hetzner auction and get real hardware, cost will be predictable and typically you get a lot for the money.