can get them from loads of retailer for around the 300quid mark, which however you look at it is steep.
i was going to buy one off ebay for 200quid but had to pull out as i crashed my car, and needed the money to pay the f**king excess.
i wont be bothering to fit one to my 172 unless one comes up cheap, as ive bought a replacement panel filter which will do for the time being and at 30quid its much better value. as the 10x cost isnt going to give me 10x the performance gain.