I have a 2006 Wee-Strom, and I rebuild my air filter using a filter for a compact Chevrolet. I forget the price Mrs. Suzuki wants for her air filters, but the filter I buy is under $8, including tax.
The work is straightforward: chop out the paper parts and make room for the filter you have bought, then glue your filter in and install your filter. Use plenty of glue, because airtightness matters and looks do not matter.
I have not seen the air filter for newer bikes, but if it resembles mine, the same notion should work. Take your used filter to a parts store and look at the rack of filters, and buy one with about the same size wad of paper, and hack away until it fits.