The maximum amount you can purchase one money order for is $1,000.00 at the USPS and you can pay for that money order with Cash, Debit, Credit Card or even a Traveler's Check.
You can get additional money orders at the same USPS location for another $1,000.00 or to total the amount you need above $1,000.00
There is a USPS money order fee of around $1.20 I believe it is.