round me it's between £15 and £20 (south-east). £20 is usually for music qualifiers. Standard classes are usually £14 to £18. No difference between O and R, or Q and non-Q.
Normally I pay around £9 for prelim and £10-11 for novice but it does depend on the venue. Also some venues will charge £11 per class and only give out a rosette if you win the class while others only charge £9 but give prize money to top 6 placings. Go figure!