http://www.aquaticeco.com/categories/Filter-Media/184/0/Filter-Media has a big selection of large pieces of filter pads that you can cut to size.
As far as locally, look for pads meant for ponds, since they're bigger and cheaper. That's what I use.
Pot scrubbies do NOT make for good particle filtration. They'll catch big pieces, that's it. If you want fine particle filtration you need some sort of pad.
They are good for biofiltration, and that's what I use them for. You really want a filter pad before them so they don't get filled with gunk, in which case you need to spray them out to clean them and risk washing away a portion of your biobacteria. Not to mention the more gunk packed in your biomedia, the less efficient they are as a bacterial growth medium.
Quilt batting is ok, but it breaks own more easily, and it also tends to fall apart and clog the holes in your tray. I personally don't think it does as good a job or holds up as well as the pond filtration pads and such. I've used it a lot because my MIL is a quilter and gets a ton of it cheap, and I'm not a big fan.
If you can get it cheap and are willing to change it often it's ok. Otherwise it isn't necessarily as cost efficient as it seems.
