Hmm, I don't think so. Cars will need GPS that includes data on speed limits. They won't need signs, because they already know where all possible destinations are and can plot a course to them without the help of signs.
That side is actually going to end up saving the government money because instead of running out and changing 30,000 signs whenever the speed limit changes, all they'll do is tap the new number into its field in a database, and that's it.
Similarly, we won't need the "Memphis, 90 miles" signs because if you want to know how far you are from Memphis, you just ask the car.
Really the only places we will need signage is in areas that have pedestrians.
Obviously, this transition will come as we reach a tipping point where the vast majority of vehicles are auto-drive.
As for who is going to pay, as I've said several times, cab companies are going to foot most of the bill. With robotic cars that can drive themselves, we won't need to all have a car. A robo car can pick me up, take me to work, then go back and get my neighbor and take him to the store. We could cut the number of cars per-capita by a huge amount, and end up with more transportation efficiency than we have now.
Your flying cars idea is interesting, but I'll point out that there are no lane markers painted in the sky, which means if you're saying that automated flying cars are possible, then so are automated ground cars. If you're suggesting human-piloted flying cars.... Erm, have you seen drivers lately? I certainly wouldn't want to be flying if the idiot who was weaving in and out of traffic while listening to noise-cancelling headphones this morning is given the keys to a flying car that he gets to control!
Right now it's hard to get out of the mode of thinking that says "a driver looks around and reacts to information painted on the street and written on signs," but robots don't need that. Check out one of the robot-staffed warehouses some time. The only markings on the floor are where humans go - the robots don't need them. All a robot needs is to know where it is, where its destination is, and the path to take to get there.
Now just add visual sensors to detect obstacles (kids running in front, oncoming non-robot traffic, etc) (many warehouse robots lack these sensors, which is why humans are never allowed in the robot area) and as a rough backup to the positioning system (I see corn ahead - this probably isn't a real road. Safe-mode stop and transmit an assistance request) and you've got the basics of robot cars that don't need all the stuff humans need to drive safely.
After all, we wouldn't need lane markers either, if we had positional accuracy on the order of microns, and we weren't a species of selfish apes who need clearly-spelled-out rules in order not to descend into chaos.