How to make cheap CO2

c02 cannot be created or desroyed. there's a fixed ammount in the universe. Honestly I wouldnt bother with those cheap home made methods. A good C02 burner is not that expensive compared to a 1000w light setup or a hydro setup. Look into it

it's a small area, 2X3X6. Short on money at the moment. I only have 4 Plants. Any ideas anyone?

I made one, you have the same size tent as I do. My container was an empty kitty litter bottle. I drilled 4 holes with a 3/8" dia bit.Bought 25' of 1/4" aquarium tubing at walmart, it cost around $2.57. Used this vid as a guide and recipe. Made it last night.
First time trying a co2 generator. It does enrich the air. Pressure builds in the container and pushes the gas out and releases it into the air. just remember co2 is heavier than air, so place your tubing over the plant so the co2 is dispersed over the plant. Is it effective? I don't know.
[video=youtube;IZFM9ZpaqGM]http://www.youtube.com/watch?v=IZFM9ZpaqGM&feature=player_detailpage[/video]

Part 2 is irrelevant, but you do see evidence of the gas released into the water

the matter is never being created or destroyed, a reaction occurs causing it to change into a different element.

yea, as in being created. a car doesnt exist as a car until its put together, but there isnt a fixed amount of cars in the universe. matter may not be able to be created or destroyed, but not only does every molecule break apart and react to become different substances (C + O2=>CO2=>C+O2), but the neutrons, protons, and electrons are constantly being exchanged. for example, i just increased the amount of CO2 in the universe because i made a CO2 producer two hours ago