CompUSA is selling these for $50, but they're on-line for as low as $30.
http://buyaleratec.com/dvshredpar24.html
As you can tell from the pictures, it does not physically destroy the disc. It puts a grid of dimples into both sides, rendering it un-readable. All you do is feed the disc into the slot. It's less work than cracking the disc (especially if you have a lot of discs), but you'd probably want to do both depending on how sensitive the data is.
Note that just cracking the disc does not solve the problem since it is possible to read data from disc fragments with the right equipment. Again, it depends on how paranoid you want to be. This device helps, but on the other hand, $50 can buy a lot of sandpaper.
