I found the treadmill cheap on Craigslist. It's not important what kind of treadmill you choose but it makes your life easier if the hand rails are simply bolted on.
I found the desk locally. I got lucky and found an adjustable desk for only $50 locally.
Step 2: Treadmill Modifications
I wanted the treadmill to not stick out, but I also did not want to put too many hours into the process.
1. Remove all unnecessary parts. I removed the hand rails, the incline motor and the hinged incline wheels. I added some black painted 2x4's to make the treadmill level (you would not have to do this but my incline motor would not stay level).
2. Modify the control panel - there was a lot of unnecessary plastic on the control panel so I took that apart and using a hack saw cut the board to a smaller size. I did have to move some of the boards around to accommodate. I don't like the look and eventually will make a new control panel, but this works fine for now. I simply used a zip tie to keep the emergency key engaged - hope I don't fall while walking!
That is all I did to the treadmill other than giving it a good cleaning and adjusting the belt tensioner.
Step 3: Desk Modifications
The desk I got adjusted from 34" to 44". To be comfortable typing on the treadmill I needed a few more inches.
1. Removed the top of the desk
2. Placed a 4x4 in between desk base and top. Screwed the base into the 4x4's and used a few L-brackets to fasten the tabletop to the 4x4's
3. Painted the 4x4's black so they blend in to the frame - does not look bad at all.