The cost of failure is around the $1500 mark.
And that's just for the CAA chap to sit with you.
On top of that would be the cost of the aircraft hire for test (around 1.5 hours) £200/$400 and if the examiner feels you need mandatory extra training then that's another £200/$400 per hour.
In other words...be prepared!
Best of luck
P.S. Incidentally, exactly how much is the flight test fee these days?