Spirit Airlines is an "a la carte" airline. They have unbundled every product and service imaginable when you fly. The Passenger Usage Fee is a fee for booking your reservation online or via the reservation center. You can avoid the fee by purchasing your ticket at the airport ticket counter. (I know; I've done it several times.) Currently, between LAS and LAX, they have hiked the PUF from $8.99 to $16.99 one way. If they aren't careful, they will outprice themselves!