I wrote on this forum years ago griping (what else is new!) about dealer prices on oil filters and I wasn't paying no 20 bucks for an oil filter. Bought Hiflo Filtro from then on. Air filters the same deal. The permanent air filters from K&N and others are the cat's meow but are even pricier so I made my own.
The first picture is what I had made for the first DT300i that was wrecked. This is the throttle body side. The wires are ss picture hanging wire about .020" like aircraft safety wire. The next photo is what the frame looks like when the paper element is sliced out with a real sharp knife.
Third picture is with 1/2" square wire screen (hardware store item) more secure boundary for the two layers of 1/2" filter foam sheet from the ATV store.