A NOS red Silverstone with metal bracelet went recently for a remarkably low £1300. Expect to pay around $3,500+ for either depending on condition. If you can find a red Silverstone with the original red leather strap and Heuer buckle you have an unbeatable combination for this watch. McQueen wore his Monaco with a black perforated leather strap so if you are after the McQueen look do not bother paying a premium for the steel bracelet.
If you are buying one in less than mint condition factor in the cost of a full TAG Heuer service at the factory (£375 - 3 months turnaround). They will service, replace hands, crystal, crowns, pushers and re-do lunimous markers but will NOT do anything to the case.