Full price for rider?

Hi there. We are doing stops at St Kitts and Grand Turk and would love to do either a dune buggy or ATV excursion. However places like Zoom Zoom Tours charge full price for both my girlfriend and myself even though I will only be driving. If tours are charging full price for the rider, we might as well each get our own vehicles. Is this normal? Most other places seem to charge half price for the rider. Can anyone recommend a tour that is more reasonable? Thank you.

Would also like to know. I assumed in Grand Turk golf cart rentals were for vehicle no matter number of passengers and thought ATV would be the same. Check with Karib. Let me know if you find out.