I ordered the parts to make a small tank rack from PVC using the plans on a scuba forum. I am just doing a 4 tank rack for my two 44 cu ft CF 4500 psi tanks. It is very inexpensive.
http://www.scubaboard.com/forums/do-yourself-diy/234816-pvc-tank-rack-plans.html
http://www.scubaboard.com/forums/do-yourself-diy/234816-pvc-tank-rack-plans.html