Like so many consumer decisions I believe the best value is to be had somewhere in the middle of the price range.
I wouldn't advise the very cheapest ATPL course circa £35,000 nor the most expensive circa £75,000. If you can find a nice little professional school, possible close enough to negate accomodation fees, that ends up costing you circa £50,000 then you have probably done well and will be happy with what you bought.
Time spent in reconnaissanse is rarely wasted!
These days it is pretty easy compared to just a few years back. Simply go to the CAA website and look at the full list of FTO's who can do all the training up to IR. Nearly all will have email addresses. Within an hour you should have been able to request brochures and pricelists from up and down the land.
Shortlist and visit.
Pay by instalments on - say - a weekly basis. Don't be afraid to complain but try to rub along. If you need to you can walk at any time.
Good luck, there are some ace smaller schools out there who can do you proud,
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