Truthfully all you really need media wise is something like a sponge, filter floss, etc. Just something to catch debris. Carbon really is useless unless removing medication out of the water, or to give it a slight polished clear look. Other then that nothing is needed. I only run a sponge in mine.
As for them being to expensive, just rinse them out more regularly, its what i do. No problems so far. Biowheels might be, but something like the Aquaclear is really cheap on a monthly basis.
Its even better for your tank to rinse the cartridges or sponges more frequently. Do it once a week. If you let it build up then when you do it, its going to play havoc with your params because you did it all at once. A little over the course of the month is better.
Whiskers i have to believe something is sketchy here. I've owned sponge filters too, and they got just as dirty, if not dirtier then my HOB filters. I never noticed any difference between the HOB and Sponge filter, truthfully the HOB was more efficient because it was pushing/sucking more water. The sponge filters collected far more wastes though being directly in the tank. I can't agree with you on them being better personally.
Sponge filters are great for fry tanks, or when paired with an HOB...but i personally wouldn't run them alone.