Just finished building a stir plate.
Parts & Source List
PC Recycling Store
24 volt PC power supply fan $.050
Punched hard drive for magnet $1.00
On/Off switch $6.49
Quick wiring disconnects $2.49
Electrical Tape $2.00
Project Box $6.99
Found Around the House
6 volt power supply from broken alarm clock FREE
Various nuts, bolts, spacers, and a washer $4.67
The on/off switch on the right...uh...turns it on and off. The knob (potentiometer) on the left controls the speed.