https://northcarrentals.com/Take a gander at their website. Try to book 10 days end of July into Aug.
As I said, found via Kayak which is where i have booked dozens of rentals for over a decade without issue. It is a prepay and probably has one of those $800 deposits (tho they dont say that) when you arrive and pay.
We barely want a car this trip and could probably survive cabbing to/from orient village lodging. Im thinking one trip to grand case, one to super U, one to the Dutch side.