My recommendation (as it always is anytime these standing desk articles appear) is the Frederik from IKEA ( http://www.ikea.com/us/en/catalog/products/60111123/ ) Ok it's not $22 but I've picked up two now on special for less than $80.
Put it on a solid desk and it isn't going anywhere. I'd bet that it's even more stable than the fredrik which has two skinny legs.
[1] https://secure.flickr.com/photos/kuno/5053375629/in/photostr...
The other advantage of using a door is that they come in various sizes (both width and height), so you can get one that matches your workspace size. You can also stain them some cool color or buy some fancy wood grain if you're into that sort of thing.