Why not just look in the Yellow Pages for a tyre supplier and ask them? To get an accurate answer you'll need to know what size the tyres are, which is stamped on the sidewall. It'll say something like 225/50VR16. Even knowing that, prices vary hugely between brands, I'd guess at somewhere between £40 for a cheap remould and £120 for a good brand name like a Michelin or Pirelli.