Well, according to all sources I can find they issued free travel vouchers - in the form of "First Moon Flights" Club cards - that could be redeemed for a trip to the moon when the service started.
According to a Wired article on Virgin Galactic (as well as Wikipedia...) some 98,000 people placed reservations and one individual attempted to pay 1 Million USD to secure his seat.
The cards, says Pan Am, are not transferable and card holders must produce them before they can buy tickets to the moon. Although no deposits were required for the reservations, one would-be passenger was so anxious to secure his place in line that he sent along a check for $1 million. The check wasn't cashed, Arey says.
"Pan Am Has 90,002 Reservations : Public Interest Grows in Flights to the Moon", Los Angeles Times, February 10, 1985. ROBERT E. DALLOS
The waiting list for Pan Am's first moon flights was closed in 1971 as the company was suffering financial difficulties and decided to remove the administrative cost of the cards. (Quote from the same article as above)
Pan Am distributed numbered cards to anyone who asked. Though 100,000 cards were printed, the airline stopped taking reservations a few years later when they became an administrative burden at a time when the airline was experiencing severe financial difficulties. It does not plan to take new reservations until it inaugurates service to the moon.
So, in conclusion, no - it appears there never was a fixed price for the flights.