The best advice would be to buy one with the mods/power you want with reciepts to back everything up. Forget mileage on the clock because unless there is a full service history/every MOT from new then it won't mean a thing. As said previously the biggest killer is rot so check everywhere! The worst place for it to be IMO is around the sunroof as new roof skins are just not available. I would budget arund £4k for a very very good example