Typical 50 hour is about £400 to £500 for ours. New / zero timed engine - I believe (not entirely sure though - someone else will have a better idea) is £15k - £20k. You've also got to think about prop time, tyres, oil costs, and a whole host of other things.
It's a very brave school that will guarantee you to pay for time they don't use - there isn't much money to made in PPL training these days, so I'm surprised - will they guarantee it in writing?
Owning an aircraft is nothing like owning a car - don't be tempted to find comparisons...
DW.