I’ll start out with a disclaimer: Do this at your own risk.
However irresponsible it may seem, making my own air filters has worked for me. I was forced into looking for alternatives for an air filter for my old Tellis vacuum cleaner. The ones they offered me cost many dollars, and I made a better one for 25 cents. I simply used new frostcloth.
I have cut a short length of frostcloth for my vacuum cleaner filters for over a year with no signs of damage. The air filter protects the machine as well as cleans the air, so it had to be perfect.
Other machines need air filters too. Most small motors need small proprietary air filters which are expensive. I have found frost-cloth to be an ideal air filter for most motors and it costs just a few cents. The weave changes between manufacturers, so be sure that you are happy that the weave is fine enough to filter out all the dust particles so none end up in your carburetor.
I prefer to examine the frost-cloth myself, breath through it, suck air through it and if it adds up, use it. Many people feel strongly opposed to this but experience has shown to me that there are low cost alternatives to buying an expensive air filter.
Air filters on dehumidifiers and air conditioners can be replaced with a quick snip of frost cloth that can be thrown away after use.
Final disclaimer: Do this at your own risk. Think it through.