Here's what I started my rain barrel research with back in 2012. I got a 600 gal. which was transported home in a SWB pickup They've got lots of distributors. I bought mine in NW Austin. It's just like Old Milwaukee - the more (read larger) you buy, the more you save.
http://www.plastic-mart.com/category/9/plastic-water-tanks
Note the weight which gives you a clue about how sturdy (thick) the side walls are. Some, evidently, are pretty flimsy. I'm happy with mine.