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=