Materials are cheap if you or a buddy has a welder.
When I built my tank, I bought 12" of extruded aluminum tube from www.onlinemetals.com
. Some of their stuff is a little pricey, but they make up for it in convenience and quick delivery. 4.5" x .125" x 12" was $20. I cut round caps for the ends, welded on a few fittings, brackets for mounting, and done. PIC
Just an idea. It allows you to save money and make it any size you desire. And there are some weldors out there that will do a small side job for beer and pizza. :-)