@fruitnut great idea. You could get those at Home Depot?

You can buy them used on Ebay but the shipping gets expensive. Look for a local source of used 55 gallon food grade barrels.

http://forums.gardenweb.com/discussions/1434923/where-can-you-get-free-55-gallon-plastic-barrels

Or you could go the fabric pot direction. They were much cheaper in the winter months but looks like they are currently running $9-15 each for 30 gallon bags on amazon.

Janitorial supply stores have been a good source of 55 gallon drums here. Usually has had soap in them... washed out, they are fine. We paid $10.00 each for them in Oklahoma, but you get two pots for that.

I work at a nursery. We have lots of clients who call and ask about recycling plastic pots. We take them back and they go to a recycling facility. However, several clients asked for large tubs to grow peppers on their patio. I always show them the recycle area where they are happy to get FREE #7, #10, #15 or #25 pots. Perhaps a nursery near you does the same. The price is right (free) and you are recycling the pot to be used again.

I use cat and dog food bags...take them apart at the seams, then sew them back together...you can can make grow bags as large as you want, and they last for years.