My Dad got his 5 Series done by a BMW dealer and it was getting on for £200. But you can buy all the stuff yourself. If you go to www.jewelultra.com all the info is on there, I gave them a ring, bought the pack with the conserver and shampoo (I think it was about £39) and it comes will all the instructions to do it yourself.
Once you've put it on, you wash it off, and it gets into all the little nooks and crannies, unlike wax and as long as you was it in their shampoo afterwards, the hard shell will last for ages and probably only needs done once a year, if that.