Servers

Used servers from previous enterprise deployments are the best way to get competent hardware for cheap. If you have the budget, building a custom PC is an option, and any modern gaming computer can make a powerful server.
~$290 Dell PowerEdge R620
~$330 HP ProLiant DL360p
~$380 Dell PowerEdge R720xd
~$400 Dell PowerEdge R620
~$470 Dell PowerEdge R620
Dell Server Image Click to visit listing.

What component stores temporary bits for active programs?

NIC HDD CPU RAM