A very easy way to create C02 for a very low cost is to mix baking soda and vinegar. The usual disadvantage is that the reaction is instant so the CO2 is drained out by your exhaust fans. A better way to sustain C02 output is to create a wick system. Take a red plastic cup that is 12 oz and pour vinegar into it. Create a wick system by poking a small hole at the bottom of a 16 oz cup and placing a few inches of yarn through it. Tie the yarn off inside the 16 oz cup to prevent it from falling through and cover the knot and bottom of 16 cup with baking soda. Place the 16 oz cup into the 12 oz cup. The bottom of the 16 oz cup should fit in the top of the 12 oz cup without hitting the bottom / vinegar. The yarn will slowly pull vinegar up and into the baking soda producing a sustained amount of CO2. Good luck and I hope this helps!