Just about every practical mechanical filter media is made from polyester. So,
Polyester pillow stuffing, otherwise known as poly fill or filter floss. The big craft stores like Micheal's or Jo-Ann always have 1/2 off coupons that are printable from the internet, so you can get a good sized bag of it for like $3 out the door (for the same stuff you'll pay $15 out the door at the LFS). The more you pack it, the more you will restrict flow. But the less you pack will reduce the particle grabbing ability.
I line the bottom with 25 Micron Polyester Felt (
link), which is the same material as a filter sock, and can also be had on the cheap outside of the LFS, in several different particle sizes (200 micron, 100 micron, etc.)
Although I will say that I have just started using the filter floss without the felt. I have about 3 gallons worth of filter floss in the mechanical part of my sump and we'll see how it goes.
Edit: I screwed that one up huh. I've not used chemical filtration in so long, that I forgot it even existed
Sorry to jack your thread.