There is Avis in the lobby. Definitely check with them a few days prior. We were able to get one 2 days out.
Rent The car directily with Avis is more expensive that with a online travel agency. The guys working there are not nice too. You need booking few days before.
When you book directly through universal (number is on the website) they ask of you need a car, just tell them yes. I know they charge to park in the hotel parking lot, but I'm not sure if they charge of you rent a car on site.
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