CO2 generator

Thanks for all the help regarding my earlier post in which I asked:

>So my question is: is there an equally cheap alternative to yeast for 
producing CO2?

I received a lot of offers for help re: putting together a reasonably 
priced pressure tank + regulator system. I am afraid I misled you a little. 
I already am using such a system on one of my tanks.

The purpose of my post, however, was to find true *alternatives* to bottle 
and yeast.