Of course every UK PPL school aims to rip off its students, doesn't it...
Charging an 'average' rate isn't that bad an idea - at least you won't get problems trying to fly all your solo hours due to instructors being reluctant to send you off and losing income as a result...
As certainly happens in some US PPL farms. Their alleged FIs only get paid for dual time, so is there any incentive for them to release you solo?
So dry your eyes and man up. All PPL schools are struggling to remain solvent, to retain FIs and to offer competitive rates; your school is undoubtedly doing the best it can in the current financial climate.