Buy yourself a new gaming rig, and use your old gaming rig as a server. That’s what I usually do.

Seconded. A few years ago I upgraded my CPU, which also required me to swap the motherboard and RAM. The old Mobo / CPU / RAM combo was sitting around in my closet. I just bought a decent case, power supply, and a few hard drives, and bam. Instant server.

As far as graphics card, I would go with something cheaper unless you have a specific reason. If your CPU has a built in graphics processor, that’s probably good enough. My CPU didn’t, so I had to throw a $30 card in.