Now you can make one much more cheap.
By hacking you can make one under 10$.
Behold the ULTIMATE SANDER!!!!!!!!!!!!!!!
For POCKET SIZED don't see steps 4 &5.
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Step 1: Parts
1. Anything that reads CD/DVD
2. Battery holders
5. Cardboard Box
2. X acto knife
3. Soldering gun
6. Gorilla tape
Step 3: Hacking Again
Step 4: Battery Pack
Also add gorilla tape.
Now Solder the battery holders together.
Then solder the switch.
Then make 2 large wires extend out.