a dealership will not/can not do a custom tune and yes it will mess with the warranty if the dealership finds out you have a custom tune on the vehicle. switching the filter back to stock is a cheap/easy cure, i recommend doing it until you can get a custom tune done. charge for custom tune varies, i've seen as low as $200 and as high as $500. it all depends on who is doing the tune and how they're doing the tuning. usually a custom dyno tune will cost more because of the dyno. i'll see who's around your area and get back to you, but in the meantime look around for a performance shop that does tuning. make sure they're using HPTuners.