"As little as possible" would be... well, not an actual number (sorry). I have somewhat of a flexible budget in mind where i don't want to spend too little and get something that performs poorly, but also not something that'll cost me a lot and i won't be able to make full use of. Probably won't upgrade it for the next 18 months unless parts with better value come along. And like i said, i'm thinking of getting an RX 570 for a GPU.
As for "what for?", well pretty much only gaming. I'm not interested in a huge leap in perfomance from previous-gen consoles, i'm just looking for something that'll comfortably run current games at 1080p at about 60 FPS. I just want a computer to play some games on, hence why i'm not looking to invest much on it.