Not sure on how big the area is you need to cover but cheap co2 can be made from water yeast sugar i hear a stronger yest like turbo yeast works best. Some people pay $40+ for those co2 in a bottle products like this one http://www.mygreenplanet.com/product/the-enhancer-co2/ and like i said above all it is just those 3 ingredients. (unless you have a large greenhouse and you already own/rent a 20lb co2 tank)
If you do a buy sulfur burner make sure it is one from a garden store and not some do it yourself burner as sulfur can give off poisonous gases if heated to the wrong temperature. Sulfur is only active for 4 hours on a burner after that it will need to be replaced.