Nice lines how many laps have you done in total? I'm guessing quite a few
The base price is 26 eur for a single lap in your own car, multi lap packs lower this down. Rentals start at 100 eur for a lap in a swift. Until you really know the way round then it's possible to have a lot of fun in swift. Actually even when you know the way round the swifts are still a proper laugh.
I'd guess that an experienced pilot could extract low 8's BTG out of a standard R. It's an experience and there is no real point in getting hung about chasing BTG times.
Just a cautionary point no current UK insurance provider will cover driving on ring during public sessions so bin it and your paying, cause someone else to bin their car/bike your also paying.