I made my own treadmill desk three years ago using a tutorial from Instructables. It is made up of a standing desk from Ikea and a ProForm 415 LT Treadmill. I bought the treadmill new for $550 and the desk used on Craigslist (as it had been discontinued).

The setup has worked great but I just moved and no longer have room for it. It's currently disassembled, but would be easy to set back up. I have the treadmill arms if you want to use it as a normal workout device instead of a desk.

Here is the DIY tutorial: http://www.instructables.com/id/Fancy-Ikea-Treadmill-Desk/ I used a bit of string to hang the controller below the desk. It's a huge savings from a full-price treadmill desk, which will usually run you $1,500.

Attached are pictures of the treadmill and the setup in my house.