itch.io

Often you can get "old" (dell/hp) desktop company computer for about $100. They usually aren't that old (~4years old) and pack a modern intel i5 CPU and 16gb RAM. You might need to drop in an cheap ($50) SSD though and a cheap ($100) low-power GPU if the integrated GPU isn't good enough.

Also maybe get the €320 Steam Deck that's currently on sale. It's prettygood value for what you get. Don't know if it has sufficient hardware for what you'll be doing though.

I'd be pretty careful with buying a computer for less than $100. For about $200 you can get a fairly nice used computer that'll last you at least the next 10 years. 

Intel i5, 8 GB RAM, 256 GB storage, and a 2-something Ghz processor are more than enough spec-wise to run almost any application and most game engines*. It's decent for gaming, just don't expect too much out of it. A lot of stuff on Steam won't run that well, but my specs are pretty close to these and I've rarely had trouble with an Itch game*.

*Unreal Engine is the exception.