Vast sums of money are a no no, even with the promise of discounts. The FBO I use will give block rate discount if you are going to fly over 10 hours but doesnt make you pay all up front.
If you are new you pay in $750 and just run it down, once they get to know you they will let you credit as little as $500 to your account and still offer you the preferential rate.
Heard too many stories of students loosing thousands. Go for pay-as-you-go, credit card or iEscrow.