Without knowing specifically what your AI requirements are I wouldn't swear on my following, but you can set up something easily for the same cost of your RAM with new components, and way cheaper if you go used.

32GB mini PCs are right around $300 on Amazon with lazy searching, which means you can find them in the $250 range if you look, and they're cheaper if you want to go lower RAM and no OS. If you have a TV then all you'd need is an HDMI cord and a keyboard+mouse, or none if you go headless. You won't need a monitor because you wouldn't be gaming on it.

But if you're going to set up dedicated hardware I'd suggest buying some server gear for better reliability in the long term. You'll still be in the $200 range to start, it's so cheap to get your first rig and make mistakes and figure out what you want later. This link has tons of lists of hardware you could put into a very capable server with price estimates. It's primarily NAS/service hosting focused so again, ymmv with AI requirements, but for base hardware that you can spin up some VMs and containers you're in business with 8-16GB and a mobo that supports ECC.

https://forums.serverbuilds.net/t/guide-nas-killer-4-0-fast-quiet-power-efficient-and-flexible-starting-at-125/667/13