Definitely not my area. But if it's a cheap filter material you need as a throw away... Recently had my pool turn extremely green so came across a guy using cheap pillow batting or pillow filling. He used it as a 2nd filtering application after the pool sand- de or cartridge filter. He just stuffed a 2 liter bottle with it and it work great on YouTube. May be a very cheap if you can rig it right. A $3 bag is pretty large and should do something. Possibly an additional hvac coil filter. Some come in a rigid composite sheet. Think that green scotch bright sponge padding comes in rolls as well.
Another idea is adding a pool cartridge filter canister before the waste tank. Not sure how great it would flow thou. Google Hayward cartridge filter canister. Canister cost not sure. The filter itself cost about $35 on Amazon. A 2 pack is about $50. Keep me posted. I need to figure something inexpensive also. Good luck