Thanks for the reply. So the tanks you referred to as cheap on Craigslist, are they large or small?

40cf bottles. approx 24"tall, about 40lbs in weight empty with a regulator...
I got two for 30.00 with regulator on them from a guy shutting down his hvac business, along with 6 bottles of 410 and 6 bottles of 22 the deals are out there. for average use, I'd think a co2 can would be better. you can get carbon fiber or spun aluminum bottles about 12" tall with a regulator that will supply more pressure and flushing capabilities then 5 nitrogen cans will... and they weigh a lot less if you have to carry them around.
ebay nitrogen auctions... not bad free shipping http://shop.ebay.com/i.html?_nkw=nitrogen+bottle&_armrs=1&_from=&_ipg=
ebay regulators... crappy deals, but still...http://shop.ebay.com/i.html?_nkw=nitrogen+regulator&_armrs=1&_from=&_ipg=

a good hit on craigslist...http://indianapolis.craigslist.org/for/1758385330.html
wow a big tank!@ http://bakersfield.craigslist.org/pts/1757646507.html
Uh... no? http://boston.craigslist.org/gbs/tls/1756813144.html