I'm heading out tomorrow (well, today now I guess) to WDW and then a 4nt Wonder cruise. I'd originally reserved a minivan through Budget for $63/day plus taxes and fees to take me to the port, and then another minivan for the day we get off the ship. It was going to cost me about $180 total for the two one-way one-day each rentals. Then we started thinking we'd like a vehicle for our full WDW stay and I priced out lots of options for different vehicles picking up at MCO or in Downtown Disney, but it was going to cost me quite a bit at $65 or $63 a day (plus taxes, etc.) to have that flexibility.
I saw a minivan at a good price of about $24/day on Hotwire for the full length of our trip, picking up and returning to MCO. Even after factoring in $60 for parking at the port, it was still a good deal. I took a chance and used Priceline, and got the minivan for $19/day through Hertz. So still a substantial savings, even after factoring in the parking at the port, and the inconvenience of using Hertz at the airport (and not getting Hertz Gold service since Priceline doesn't let you get gold service on their rentals.)
Obviously I haven't picked up the car yet to know if there are any unexpected problems, but I've used Priceline before for rentals without any problems. This is the cheapest I've ever gotten a minivan for though! Obviously it would have to be super cheap to cover the 7 days of your cruise, but the savings in my case would have been substantial enough to cover the extra $45.