A:Answer What I would suggest at each price: (Keep in mind these are AMD only, if you want intel, then you would need a different motherboard. With all of these, you should get 16gb of ram. This PC is upgradable, just check the dimensions of the GPU you want. It may not fit. The 1600 AF may look old, but it was released around 2019.
200 and below: Doesn’t make sense to upgrade, parts are already good enough.
250: Keep the 3100, upgrade to 1660 super.
300: Upgrade to a 1600 AF (Make sure it’s the AF refresh,) 1660 super.
400: Keep the 1600 AF, get a 5600xt, or 2060.
500: Ryzen 5 3600, 5600xt or 2060. This one’s a stretch, but 1600 AF + 3060. (Better for AAA games at 1440p and above, the 1600 AF may bottleneck at lower resolutions with esports games.)