If you are after the price then you bes bet is to contact the dealer who sold you the car they are the ones most likely to know. I'm not sure who would be manufacturing the kit but my guess is that its made by Pipercross, as they make the kits for the JCW S and the challenge Cars. if you are worried about the warranty then you best bet is the JCW stuff as you will keep your manufacturing warranty.
If however you are not conserned about the warranty then there is a number of options that you can go for:
1- Pipercross Induction kit which retails at about 90 pounds.
2- Pipercross Viper kit - 250 - but very good gains especially if you want to do more engine mods like chip,exhaust and ECU
3- GruppeM (if you have money to blow)- amasing kit using a K&N filter inside a fully carbon fibre air box and v. good gains like with the viper kit
4- Any other kit from the likes of K&N, Greeen Cotton, Alta, Rouge Engineering, and anything you really want it all really depends on what you are after POWER or LOOKS.
Give guys at lohen a ring they can sort you out - 01785 761300