A barebones, back of the monitor net top runs around $150 or so appears to be exactly what they're using:
http://www.newegg.com/Product/Product.aspx?Item=N82E16856119...
Then throw in a small HDD or SSD, a monitor, RAM, keyboard, mouse, and you're still at or below the $350 mark. These computers will get even better as the low-end battle between Intel and AMD heats up, and ARM alternatives appear.
I set up a bunch of systems like this that PXE boot into Debian off an older server last week. They run great, are nearly silent, and take up less space than the aging G3 iMacs they replaced.