none of us can really afford to pay for the entire trip anyway. (Still in highschool) . Usually we start off with an empty tank...and we will just put in , 15$ or so per person, depending on which river we are going to. If we put in to much, the driver will just pay the amount owed back, or if it is too less, everyone will put in more. Gas this summer is really going to suck. 4 people in a car getting 24 mpg, will probably cost 30$ or something, with the way prices are going up.