Found on CL...

Three Oxygen tanks for $99.

I know nothing about these tanks at the moment, but can tanks be used for other gasses? In other words, can an O2 tank be used for CO2?

99.99999% positive that even if they COULD (like, they have the right threads and such), you would not be able to get them refilled with anything other than O2. Too dangerous otherwise.

Figured as much... thanks bird

There is a chance thought that if you took some oxygen tanks to the local welding shop that they would exchange them for CO2 tanks.

what size tanks? i assume at least 20 CF tanks, and at that price, it's almost a steal (if they are still in test, if not, that would be another 60 dollars tacked on).

find your nearest airgas, and ask if they are willing to trade tanks. tell them what tank you have, and what you are looking for.

i recently did an exchange of a 5# aluminum co2 tank for a 20 CF steel oxygen tank, as an even trade, so i just paid for the fill of the oxygen.