Just keep looking, you will be amazed by how many things will look like forge bodies. Mine is made from a 15 gallon steel drum that held racing fuel. It took some work to get it shaped and sized right but it works well now. Paid $4 for it and met a nice group of guys at the same time who happen to also be interested in knives.
Recently there have been two different hot water heaters set out along the side of the road for pickup. They would probably make good forge bodies after some resizing and shaping.
Keep your eyes peeled, keep asking around, there are all kinds of things out there that can be made into a good forge.
Chris