I've rented boats at both DTD and OKW.
Half-hour rentals start at around $30.
Since the boats are LOW horsepower, it takes about half an hour from DTD to POR. At $60 per hour you would have a VERY expensive shopping trip.
Besides, I don't think you can rent at a resort and dock at DTD and return to your resort. I remember that the rentals had to be returned to the point of rental.