I have used these in my class for several years. They are cheap, solid (the only one that ever even got bent had a rather heavy student fall on it during a fight), and easy to set up and break down. They are ideal if you have to do this in your classroom. If you have a permanent keyboard lab, you may not want to go this route.
Quik-Lok T-10 Keyboard Stand
The manufacturer's warranty covers parts for five years and labor for five years from date of purchase. The warranty excludes damage from misuse, abuse, and contains other exclusions.