I have not TRIED Priceline since last spring.
But, starting -- maybe a couple of years ago -- I found that in naming my own price (bidding) their rental car prices were absolutely not competitive at all. Even trying the old last minute before you leave for the airport bid did not produce any savings from what I had been finding online myself.
And you do know that they just "Killed" bidding for flights on Sept. 1, meaning you can't NYOP for flights anymore.
The rumor on travel sites is that bidding for car rentals and hotel rooms will soon end also.
So, just thinking, it is not a profitable model for them anymore.