The person giving you a ride is offering time at both ends of your plan.

The cost of a ride is not really the minutes spent in the car. Someone left earlier than they needed to, waited somewhere, rearranged an afternoon, and will drive home afterwards with nothing left to do there. What you received was a shaped day, not a short trip.

The next time someone drives you, be ready early and be clear about when you expect to be finished. When you thank them, thank them for the waiting as much as the driving, since that is the part they gave up quietly.