I've used 15 gallon? clear storage bins (the 3 pack ones from Costco) for over a year, filled nearly to the rim, some top on, some top off (plants only) and with a HOB hanging on the long side. Yeah they bow a bit, but never had any problems, even after a years time. Although I am sure the thickness and construction of the bin has a lot to do with how well it would hold up. Don't try carrying it (or even sliding/pulling it with one hand) with too much water in it though haha, broke off some handles/rims that way.
I have seen round clear storage containers, but none very deep. They would be more rigid, but would have a hard time trying to mount HOBs if you wanted to use those. Now is the best time to find storage containers (many people use them packing away Christmas decorations). Check Walmart, hardwares stores (Home Depot, Lowes, etc.), Big Lots, etc.
Heh, for the price of some of them, might as well buy glass tanks (used or on sale).