I suggest you take the train to the car rental place there, it is easier to take the bus to the airport again.
I think I understand your question. U save has a shuttle service from the airport. You NEED to go to the car rental center at the airport. Outside at the parking lot, the shuttle comes about every 20 mins or so. Just be ready to fight to with them to get your deposit back. They add on a $250fee/deposit. I had to make 3 calls to get a refund.
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