Small DC Frame Sizes
- $6 for 24V, 1000RPM - 15W - 
- 550, 775, 895 - etc frame sizes - 
- Ex. 775 motor - 150W - 
- Ex 895 motor - 360W - $17 - 12000 RPM - . Good power but fast.
- 150W for $12 - 
- 14W - $6 - 1000 RPM - or slow, down to 22 kg-cm . Cheap but too low power.
Using Existing Drills
- Corded drills may be used as a power source.
- Cheap option, for good torque - 600W. $30 off the shelf. 
- $15 for 3/8" drill - 300W - 
- Best option for powering a shredder- use common drills.
- The best option for the money, $50 for 3 hp. 
NEMA Motor Sizes
- This page explores sourcing for various electric motors
- Summary: 4 hp treadmill motors (high voltage DC) are the cheapest replicable source of motors per horsepower - at $20 per horsepower. Next is 5 hp compressor motors for $180, or $60/kW. Interesting, the surplus treadmill motors are a win. Since they are 130VDC, you could rectify regular wall power or use batteries
BLDC Hub Motors
Best price per kW for motors - $70/kW
- 3hp AC - $30 -