Though I personally love stock tanks for making an aquaponics system, I just wanted to show you reasonable prices/sources for IBCs and 55-gallon barrels.
Novabarrel is a source local to me here near Washington DC - I can get 55-gallon barrels for $35 or IBCs for $145 (he only has one in stock currently, but expects another dozen or so in the next month). An IBC system (3 IBCs (~$435) cut into a tank, three growbeds, and a sump) could fit in the 10 ft. x 10 ft. HomeDepot greenhouse ($250 delivered to your door). For those in the middle of the country, you can find used IBC containers via eBay, Craig's List, and web searches.
When I was considering a system using 55-gallon drums, I came across a guy in New Jersey who has thousands of the things - blue, green, and white.
One note of caution - the white/translucent barrels and IBCs break down in direct sunlight. You'll want to paint these, unless you need them to stay white/clear for some reason.
The reason I was researching novabarrel again is I'm in search of a white 55-gallon drum so I can make a black soldier fly (BSF) composting system. You can see the 55-gallon drum design for BSF composting at GardenPool.org. BSF larvae power through food scraps, so you get compost faster than standard methods. Plus BSF larvae are good eating for the fishies.