If you're in an area serviced by CitiBank, they have a "milage" check /debit card (Mastercard logo). SO you're still spending your own cash, but get miles for it. There is an annual charge though: two levels. The cheaper one is one mile for each two dollars spent, the more expensive (annual fee) is one mile per dollar.
They also issuse credit cards with milage on American. Most of the milage cards have some sort of annual fee. You have to decide if it's a better deal to pay US$50.00 a year for the card and get miles, or just pay the $50.00 for the tickets...
Good Luck
Scott