The Emira driving experiences are now on the Thruxton web site... £275 for 3 laps in a Cayman and 4 laps in the Emira.
I like Thruxton a lot, having driven there a number of times, but to be honest you'd get better value at the Lotus Acadamy (not a sentence you see very often!) - I paid £180 for 2 sessions at Hethel (both in an Emira obviously) 3 laps in the first session (the instructor drives first so you know which way the track goes), then 5 laps in the second.
Compared to other experiences at Thruxton, this seems expensive - I paid £279 for a similar number of laps in a Cayman/Mclaren.