When I have done one way car rentals in the US, I have always been surprised at the fee the car rental company charge you for not returning the car to where you collected it from. I did a road trip around Mount Rushmore, Yellowstone, Grand Tetons, Salt Lake City, etc. I collected the car at Denver and returned it to Phoenix and the one way fee was $500, which is circa $1 per mile.
Maybe they have special arrangements for Route 66 as know one will drive both ways...
