If heats not an issue then propane is the cheapest source to make CO2. Never used the stuff your thinkin of, but I use a very small propane torch in my flower room which is small...can't use it in the summer due to heat issues tho. I just run it for 15-30 mins when I'm home as it can be quite dangerous to leave it alone burning. Using it for veggin is a waste, IMHO. It does make a substantial improvement in flowering tho.