Nearly 20 years ago I purchased a 1972 full-factory-sunroof R4 and this came with its original purchase invoice dated 24th June 1972. The basic price was £621.20, to which was added a supplement for the sunroof (£43.50) and — interestingly — a surcharge for individual front seats (£20.30). Evidently the now-sought-after bench front seat was standard in those days. With various odds + ends plus Purchase Tax the total came to £871.74.
Prices rise. The thing is still in my garage having only covered a few hundred miles since I bought it. We're probably talking about £4500 these days.