I've been obsessed with finding one of these ever since, but they seem to start at $500 -- which is too much for a chair for me. If anyone can suggest an economical alternative, I'd love to hear it!
This way, I got to feel out a standup desk for no cost, and got to experiment with different heights and configurations before I invested in one. For example, I initially thought I'd want to get a tall stool for the times I was tired of standing. After a few days with my standup desk, it never even occurred to me to sit.
Once I knew I loved a standup desk, and knew what height I wanted, I found the Ikea UTBY desk to be just right and super cheap: http://www.ikea.com/us/en/catalog/products/S49843462