I use the Edsal heavy duty shelving for a double stand for 40 breeders. You can get 2 stands (enough for 4 tanks) out of one $65 set of shelves. I did a build thread on the set up a while back.
Not the prettiest stands in the world, but certainly affordable and easy to do. The only downside that I know if is that you cannot get the bottom tank out of the stand without first taking the top tank off. The tank fits perfectly down in the angles in the shelving unit.