What should he have said when he was told to pay for his portion?

My son was invited to a high school dance by a young lady from another school. When he arrived to take group pictures, he was told he had to pony up for the limo and for his share of dinner. He ended up spending nearly $80 to go to a dance with a girl he barely knew.

I've always told him that his obligation upon being asked to a dance was just to be a good date: purchase a corsage, offer to drive, dance with the girl he came with, and thank her for a great evening.

Has something changed? What should he have said when he was told to pay for his portion of rides and dinner? Why do kids order up limos and dinners they can't pay for themselves? What's wrong with a potluck and a ride in Mom's car?