I know there was a thread on this subject before, but I can't find it now...
Anyway, go to eBay (http://www.ebay.com) and do a search on "geocache".
Always some interesting items there. Great buys on ammo cans - bids starting at one penny - but shipping is $10! Sheesh!
And there's a VERY well stocked Army surplus store in Newport that has ammo cans for $4.95.