We have a Emerson Quiet Kool air conditioner in a

you can actually make a filter for a lot cheaper,
anyhardware store will carry the filter material on a roll, or bolt, just but the thinnest stuff and cut it to desired size.
many times I have bought Mezlin from a Crafts store, it is very good filter, and has almost the exact permeability as most of your ac filters

hope this helps