I know what you mean! the media can be expensive, but guess that is the case with any filter system. I ran my first tank up fishless, doing away with the carbon pad, (boy they are expensive!) only used these if chemicals needed removing from the tank water, and keeping an eye on the prefilter foam, cleaning it with aquarium water regular,( these last a long time, longer than the 2-4 mnths they advise for replacement) any decomposing plant bits etc not good for biomax and the bacteria, they like clean water passing over them.
I have an external Fluval filter now, that has more capacity for the bacteria, and doesnt take up room in the tank.