After much anguish I sold two of my bikes and bought a Bike Friday custom fitted to me. The reason that I did it is because I was struggling with the same issues as you. With regard to rental cars, I have only rented in England, the price of a rental vehicle that will hold two full size bikes is literally 2 1/2 to 3 times as much as a compact car. I figure that the Bike Friday will pay for itsself (eventually) by savings in car rentals and the fact that I won't have to shovel money at airlines everytime that I transport a bike within the U.S. If only somebody could figure out how to put a bike in a giant golf club bag we could take them along on airplanes for free.