The cost per hour is much less important than the number of hours the PPL "takes", and how confident you are flying after getting through that one test on one day.
Talking around, it seems 45-85 hours covers most people training in UK weather, so anything that improves your learning experience per hour is important.
Concentrating the lessons may help, eg two lessons per day, lessons on successive days, etc. As you get to do things solo, it helps to go solo in the afternoon if you just demonstrated the skill with your instructor that same morning.
Sadly, one thing you will never learn on the telephone to the school is their attitude to cancelling lessons. For example if you have mastered circuits except for the flare and landing, and the wind is 20 knots, gusting 35, you might not learn anything useful doing another six circuits. If it is a typical UK March you could spend 5-10 hours not learning how to land. But will the school tell you that? The school covers overheads every time you fly, the FI gets another hour every time you fly...
This is not a rant against hour-building FI's. The FI for my PPL was a young, inexperienced hours-builder waiting for a job with the airlines. He was also extremely good!
So my two cents worth is be ready to change schools if you get stuck in a rut. (Talk to the school/FI first though). Another reason not to buy a package.
Good luck!