Weed pays for the filters, and if you're growing your own, why would you buy any pot? And if you're not growing, why would you need a carbon filter? Basically, indirectly, I exchange a quarter ounce of pot for a carbon filter. A quarter ounce of pot costs me about a dollar to grow, sooo...I get a carbon filter already made for me and filled with carbon, with perfect flanges for ducting, for a buck. *looks in wallet* Yep, I can live with that cost.