Ok so you want a ghetto CO2 set-up?
Here it is:
You need to locate a store that sells supplies to old fucked up people. You know, the ones which sells wheel chairs and medical supplies.
This is what you are after first for your first ghetto CO2 set up....an I.V. bag. An intravenous bag with a plastic drip thingy to regulate the drops. They are pretty cheap. If you know someone who works at a hospital or doctors office you may be able to get one that way as well. They are not illegal so don't worry.
Next you need to buy a gallon of vinegar and a box or a few boxes of baking soda. These ingredients are real cheap. The cost is under $5.00 or so and certainly under $10.00 total. The IV bag may come free or under $10.00 as well...they are cheap.
Fill the IV bag with vinegar and hang it up on the wall or secure it up somehow. Let the vinegar drip into a huge bowel of baking soda (this means something to hold the baking soda with little rim).
As the vinegar drips and hits the baking soda, it will make a little fog. That fog and reaction is CO2. You have created your first CO2 generator which gives off no heat or smell.
Remember your fog needs to be elevated above the plants or a small fan should blow on the baking soda to mix the CO2 up in the air. CO2 is odor less and invisible and heavier than air so it needs a little help to move around.
That is it...simple effective and totally ghetto.