How about the larger commerical grade plastic trashcans that HD and lowes carry? My neighbor can get you some 55gal steel barrels for nothing, but then there is the rust issue. As for wooden barrels, I saw them in Nogales, Mexico last summer for 10bucks, but they would take $5 a barrell if you bought at least two. Good Luck on the search.

Go go your local drive-thru car wash and ask for their empty barrels that soap comes in. Around here they are white. They will usually give them to you if someone hasn't already asked for them. If so, put in your request and check back often. They go thru them pretty quick. MM

I work with community gardens in urban lots. Rainwater collection is essential, as these lots have no city water access. There are several olive importers in our outlying industrial areas that give away the large plastic drums with screw tops they use to import olives. (By large I mean about 3 feet tall.)
Good luck.