If you have no problems with high heat, I wouldn't waste the $500. You can get great results from just making sure you have fresh air available and flowing constantly. The plants can only use so much CO2 and fresh air has all they need.
The higher the temp, the more Co2 the plant can use. . . thats where the benifit of added Co2 is. If this isn't your case, I think you would do well by just keeping adequate ventilation, and cirulation. What kind of setup do you have?
500 is a little steep but i love my c02 set up, much more productive and greener plants, noticible pretty imiediately. As for fresher air i just have the co2 and fans set up on timers as to not interfer with eachother.