I have a Macintosh 8500AV upgraded with USB and Firewire, together with keyboard, mouse, monitor, and extras that was used for years in a sound studio. Loaded with sound software and could still be used to master digital recordings. Great working order. $100.
I also have 3 PC Towers, complete with monitor, mouse, and keyboards, all running Windows software. Your choice, $50. Call for an appointment to see.