At the risk of stating the obvious.......
NEVER, NEVER EVER PAY UP FRONT!!!!
If you can get a SMALL block at a discount, it may be worth considering, but always work on the premise that the school is going to fold and take your money with it....so only prepay what you're prepared to lose!...It's a huge gamble, as many really well-established training organisations have gone down the tubes , over the years.
If, at 16, you have managed to save that much, you are either very industrious, or have extremely genorous relatives/friends....either way, it would suggest that , over the next six months ,you can save some more.
It's an excellent idea to do your ground-studies first....costs verylittle and gives you a much better idea as to what any air-work is about,so you'll get much better value from that.
a bit of lateral thinking....have you considered Glider-training?...It's generally considered to be highly beneficial (look up Gimli Glider and Chesley Sullenberger as prime examples.
Good luck to you!