When you look at what is available in the 2 seat Roadster marketplace I'd say £25k to £30k is, for a car of that performance, not unreasonable.
A used 981 Boxster would be a good alternative, is available with an automatic box and has a powered roof.
The advantage of the Rocketeeer is that it has a new engine and largely restored mechanicals. A high mileage 981 Boxster could be a bit of a money pit, especially if the intermediate shaft hasn't been re-bearinged.
I'd say that his market is someone who doesn't want a Lotus or a Porsche....or a Morgan...or.....