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.