I saw that deal too! It looks pretty good. I found a 7 lb tank on ebay for about 40 dollars. It's an odd size, and I knew I'd have trouble finding someone to trade it in, but I emailed tuxedo park brewers, and they said they'd be ok with me trading the 7 lb in for a 5 lb tank. I figure, it's basically like getting a filled 40 dollar 5 lb tank, and that's still a pretty good deal.
I'll also definitely call around the fire extinguisher places around here, I'm sure they'd be more likely to have more reasonable deals than the welding places.