Welcome to our humble forum Andy
Key to the S30 is research, whilst simple in concept after nearly 40 years most UK cars have undergone various degrees of surgery to keep them on the road.
A "reasonable" UK car (no major rust, lightly molested etc half decent paint) will fetch £6K upwards
A "project" (bought without knowledge and prior to the "oh sh1t" moment) can fetch as little as £3K but be prepared to spend considerable amounts on getting it safe never mind acceptable.
A total restoration will cost £10-£15K and lots and lots of time, oh I mean lots (several hundred hours)
Certain parts are impossible to find (inner wings, some trim, wiring looms, dash etc) mechanicals used to be plentiful but engines and gearbox's are uncommon making the whole job more difficult
Then you have the issue that only a few hundred 240/260's still exist in the UK making it rare with a reduced(ing) pool of spares.
But get past the economics and it is one of the most enjoyable sports GT's around, with a well sorted 240 easily holding its own against "modern" cars in terms of performance