You can book your plane tickets and go to the airport or city ticket office to pay cash for them and pick them up. Perhaps a friend or relative with a CC could charge the tickets on their card and you can pay them in cash?
Hotel rooms at WDW you can book, they send you a reservation slip and you can mail back your deposit with a MO.
The car is going to be a big problem. One or two of the agencies will take a cash deposit, but it's $500, they run your credit and if you don't qualify you do'nt get the car. It has to be taken care of in advance. At WDW you don't really need a car--you can take a shuttle or car service from the airport, and WDW will get you anywhere on property that you need to go with their system of buses, boats, and monorails.
Anne