The units I'd use are:
Lenovo ThinkCentre M57e 6305
System info:
CPU Intel Pentium E2200 / 2.2 GHz
Number of Cores Dual-Core
Data Bus Speed 800 MHz
Chipset Type Intel G31
Sata SSD
4x 1GB RAM DDR2
No Monitors
Cost of Hydro in my city:
OFF peak$ 0.065 / kWh
MID peak$ 0.095 / kWh
ON peak$ 0.132 / kWh