Do you already have a treadmill? If not, grab whatever quality you can afford from craigslist. I didn't do any electronics hacking on mine. I took a few trips to Home Depot to buy misc hardware for the monitor mount and keyboard base. It was mostly a result of trial and error taken one piece at a time (monitor mount, then keyboard mount). Feel free to contact me directly if you want me to look over any mockups or have any other questions.

My big regret with my treadmill desk was the noise level. Definitely test anything before purchase to see if you can comfortably talk over it and think without distraction.

I think most decent quality treadmills tend to be noisy. I use noise canceling headphones to listen to music (or nothing) when I'm on the desk.