Looks like it is about $4 for both the foam and the carbon, but the foam can be used twice. So really $2 a month and an additional $2 every other month. Not too bad considering I was paying $1 a month for cheap carbon for the pf10. I am more than willing to do that to use the better filter and have better water quality for the fish.
On that comment I disagree as I found that I can pack poly-fil to the density I need to achieve the same clarity and quality. Using it for the best effect still brings me in a $4.00 a year per filter. You really need to use the method that gives you the most confidence regardless. I also have the luxury of free time that many people don't have. I was able to utilize that free time to show me what worked best and at what rate. I was also able to use it in canister filters as well to prove its efficacy. I have used it in, corner (box) filters, HOB, (Marineland) HOT, canister and wet/dry (trickle filter). I have also used in in conjunction to UGF's.
I started on the quest do to having too many different filters and having to keep a large variety of cartridges on hand. So I found a "Fits-all" that works! Hope you get your free things and don't end up getting hosed.
P.S. I agree about the AC sponges, they last forever!