I've gotten pots matching this description from both Walmart and Costco. I think they were about $25/each. Unfortunately I think they only stock them during spring and summer, at least here (northern Virginia).

I bought a couple of 25 gallon pot shaped containers at one of the big-box-home-center stores in the pond section of the garden center. Another possibility would be to purchase a food-grade 55 gallon barrel and cut it in half. If you know someone who works at a large bakery or a factory that makes food products, they can often get them for a few dollars.