1. Do they cover the sitting and standing range (or just some variable sitting range)?
2. Can you adjust the height without taking everything off your desk?
Regarding 1: There are some desks with hand cranks that may be marginally cheaper - but the ones I can think of right now don't cover the standing range, they are only good for sitting positions for people of different heights.
Also, while there are some possibly cheaper ones, they look so flimsy and poorly constructed that I wouldn't recommend them for serious work, e.g., the frame is so weak that the desktop just wobbles and shakes at the slightest touch.
Regarding 2: Many cheaper desks have pin-based mechanisms. I used to have the Ikea Fredrik desk (http://www.ikea.com/us/en/catalog/products/60111123), but I found that I never adjusted it, because taking everything off was too cumbersome. Then I had it at a standing height, and found standing all day too uncomfortable.
I will keep my eyes open and add more desks as I find them - if you come across anything, please pass it on.