Start here http://www.ferrarichat.com/forum/206-246/536402-246-gt-rhd-coys-alexandra-palace.html then try a search on rhd in the Dino section for other references .
There are quite a few GTS Dino's for sale here Used Ferrari Dino cars for sale with PistonHeads but you will have to e-mail or ring them for a price as they all seem to be POA. My guess is they would be asking around £450,000.
Thanks Grant, Was wondering if we could trade the Dino for a F40 and TOP up. F40 prices are pretty strong still
This one goes to auction this coming weekend (no affiliations) https://www.silverstoneauctions.com/1973-ferrari-dino-246-gts