well when enritching a room with CO2 there is a pretty simple solution.
Try this: instead of buying CO2 bottles you could just create it by yourself using:
Water,Yeast and Sugar. Yeast transforms sugar into alcohol and a byproduct is CO2.
So take a fermenting bottle, make a sugar/water solution, darken the bottle (UV kills yeast), put in the yeast (fresh yeast works best for me) and voila.
So next thing would be a tubing to bring the CO2 to the buds.
This is by far the cheapest solution, and if you like alcohol you have a perfect alcohol for destilling later.