The stock air filter pulls in air from a very clean location so they last a long time. The cone filter attaches directly to the tube going down that has the MAF sensor in it. No cutting necessary. You can see what I mean easily by getting under the car and looking. I warmed the cone filter end so it would stretch just a little and a 3" I.D filter fit easily.
I should note that at 121,000 miles my air filter didn' look all that dirty, peering into the inlet side. Blowing into the filter housing the direction air would flow, there was quite a bit of restriction. The indicator was still in the green.
As far as I know there is no (reasonably priced) replacement air filter unit other than the cone filter replacement.
Thinking more about this, I believe the stock filter housing is made of ABS plastic. The same stuff black plumbing pipe, and it's glue, is made of. Replacing the filter MAY POSSIBLY be done this way: Cracking the stock filter housing apart and removing the stock filter media. Securely gluing a short 1" section of 3" ABS pipe (3.5" O.D) to the inside of the outlet of the stock box. Install cone filter onto the glued in pipe when cured. Would take some fiddling to get the right cut of pipe and filter combination to fit inside the box. I would also glue in some reinforcement plastic to this joint. Assemble both halves of the stock box back together and re-install the complete system.
This is just an untested idea as far as I know. If it works it would look and sound very nearly stock, but flow like an aftermarket. Also, as I said it pulls air from a very clean area of the car, so the filter should last a long time between cleanings.