Two ways to crack the nut:
1 - If you have sufficiant savings to cover the cost of all the hours you want to block buy, pay by credit card, then pay the full amount on the cc statement each month.
2 - If you haven't got the cash, get a bank loan, (some are giving them at rates as low as 7% at the moment), stuff it in an interest bearing cheque account , and pay off the full amount on the credit card statement each month.
You'll still end up paying interest on the money owed on the loan, but it'll be a lot less than the credit card interest.
Never, ever, pay a flying club up front in cash.