Yes, there are on-site auto rental agencies but you save time & probably money if you would suggest reserve an auto in advance on Rentalcars or Kayak or Skyscanner, for example.
Yes pricing is different with each company on hand
If they don't have one, Uber to a uhaul location and rent one of those
Yes you can rent a car there but we got lucky that they had one available. It's better to do it in advance.
Each rental company is different, they do offer discount for corporate and others. You can go online to compare pricing
You can rent a car there, but I don't know the prices, I apologize
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