I have put a polyester pillow in my sump to polish the water it is working very well it cost me $7 AU about 1/8th the cost of polyester "FILTER WOOL" from the LFS .
Just thought i would share that .
you can buy rolls of the stuffing, usually for much less than the pillow itself. i buy big rolls of poly-fill for like $5 USD. and it lasts me a while. the other benifit of buying thr roll is that you can cut it to the size/shape you need.
Since you quoted au currency, i will assume you are in Australia. Use places like Spotlight to source polyfiber matting/fill. Even cheaper than your pillow.