What does it do?
It takes an object and scans it to a 3d file.
Using an 10c reflective IR led pair, Spin to Win scans a 3d object from the side by continuously rotating it and changing the scan height. Then we map out these points to a 3d map using WolframAlpha and generate a file that you could use to 3d print an object of your own.
Is it really under $20?
Yup. $7 for the top servo, $0.10 for the reflective ir, $3 for the dc motor on the bottom, the cardboard is free, breadboard is barely used, could get a small cheap $1 one, arduino clones are anywhere from $3 to $20, generally around $10 for those with the same microcontroller, and the gears came in a $3 kit with way more than these. Electrical tape can be bought for $1 per 2 rolls at dollar tree.