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Built this treadmill desk for about a hundred bucks. Gets me up and walking while I work which has been great.
Used 2 and 1.5 in PVC. The legs extend for height adjustment. Ikea sells the desk part for 15 bucks and the leg attachments I found in the 1/2 off bin. Didn't end up needing Ts for the feet and could have just used a 90 degree elbow. Routing out the 1.5 to 2 in reducer for each leg was difficult and would recommend a sanding brush drill bit to do the job.
A couple months have passed....
Recently I added some http://store.hermanmiller.com/ Flo Monitor Supports. They are lightweight and easy to attach.