Probably £70 - £100 per half rail = possibly £300 / £400 for both sides. But it is very easy to DIY For the price of the mastic strips some new s/s screws and several hours removing and cleaning and maybe a few beers for your mate who helps. Plenty instructions and pics on this website.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.