i have seen quite a few people make their own using all kinds of random things.. here is a good example where a guy used a concrete mixing tub from lowes.. the thread is diy ebb and flow table for under 50 bucks! looks like a fine setup.
http://www.icmag.com/ic/showthread.php?t=70262
I have also seen people use osb board and pondliners. that would work but you would have to be careful to make sure there were no leaks. i'd rather use a plastic tub right off the bat than mess up and have to redo it. try googling diy ebb and flow table and see where that takes you. maybe check ebay for local listings where you could go pick up a used one somewhere near your location, or any classifieds you can think of where people might be selling a used table. There are a lot of options, just be creative and keep it simple..