Yep, Gfink is right, you don't ever need to change out a bio-wheel unless it gets damaged, or if it does gunk up to the point that it impedes its own motion then all you need do is scrape off the gunk and its good as new (well... colonized/mature
The same applies for sponges, use'em, rinse'em and repeat till they fall apart. I'm not sure about the cartriges, no personal experience, but a friend uses them and there are threads here and at other sites about re-using them.
My friend re-uses his, he just rinses them in tank water or uses his water hose nozzle to blast'em clean (He only cleans on filter at a time this way) and he also cuts the carbon out of'em. I've heard others talk about disassembling them and using floss, sponge and various pads in them. Just open'em up, take out the old, put in new and rubberband'em together.
After almost a year the bio-wheels on my Penguin 330 are still, well, like new!!! I thought they're supposed to get gooey by the 'bios' taking residence on them??? I have a rather light bio-load, 55 gal with 3 angels, 1 guppy, 3 neons, 6 zebras and two CAEs.
On the other hand, the catridges are really dirty now and according to the manual it's time to replace them.
Has it been a year since you serviced/cleaned your filter?
Tell me its not so...