FI(R) between 5 pounds an hour plus retainer -15 pounds with no retainer.
FI between 10 pounds an hour plus retainer of approx 25 pounds a day - 25/30 pounds an hour no retainer.
Skill tests about 150 pounds all in.
The above are for an average PPL flying school.
Sorry I'm in the states and there isn't any pound sign on the computer!!!
Good luck with your instructing