It costs between $400.00--$1,000.00 for a decent CO2 system. The atmospheric ppm meter is $500.00 alone.
Much more cost effective--provide excellent flo-thru ventilation, which you'd need before CO2 augmentation anyway.
My plant said to me, it said, "No more for me man, I'm drivin". Hey no shit man, the fuckin plant was talkin. Hey, hey, one time my dog talked to me. Boy was he pissed. He finally told me why he, (a Chihuahua), danced around all the time like he was freakin nervous; he said to me, he said, "Hey, you'd be nervous too if your bladder was full with two drops!" Hey, you wanna talk, lets go out on da lawn. I only gotta move once in awhile then". I think that was when I was takin that acid in Berlin. I loved that dog.