Oh, I know there is certainly some sort of warranted fear. But not $150 one-way fear. If the $150 was for Round-Trip service, than I maybe could see it. But even still...
It's going to cost a family $300 round trip since you're choosing this option. I can rent a 5 seater compact car for $66/day in Orlando now. If a family is in Orlando for 5 days, the total expense for the car is only $330.
I think Disney is really hoping that either...
1.) there's enough families who are frustrated enough while at the airport that they'll pay whatever they have to
or
2.) While booking the vacation, the child will see promotion of this COOL service where you can ride from the airport to WDW in a car that looks like Minnie! And how can Mom and Dad say no to their little Princess?