AMD Athlon II cpu 3.1GHz - ADX2550CK23GQ 64 bit
Dual core, energy efficient, runs very cool. Socket AM3 or AM3+, may also work in some older motherboards.
$45. Bought new OEM, never got around to using it. Works fine and will be shown working.
Heatsink/fan not included but could be provided for $5 extra.