Reputable schools won't insist on pre-pay unless you're hour building and looking for big discounts
Even then it is possible to pay as you fly, and then pick up the discount as a nice, fat reduction off your CPL and IR. Truly reputable schools give you a discount for booking in advance and flying a large amount of the training with them (because aircraft that are flown a lot are genuinely cheaper to run, and that is only possible with a lot of pre-booked flying), not to keep their cash flow and impress the banks.
I put my hands up: I made the error once, and recently had to pay well over £2000 to do the training I had paid a certain company for, before they stopped trading. Fortunately, although I also lost a job with that same company, I could afford the loss and my current employer helped me to do so by their easy terms and staff discount. I have friends who could not afford what they lost.