We use Priceline a lot for rental cars. As the others have said, the taxes and fees are not included in your bid, but they are the same that would be added by booking through the car rental company itself (except for the $5.95 Priceline fee). I find the best rates I can (typically through Orbitz plys some messing around with coupon codes), and then bid below that. We usually end up with
Alamo or
Avis, although we did get Hertz once (the others are onsite but you have to take a bus to HertZ...ended up working out well, though, as Hertz upgraded us from an economy car to a Rav 4 for free!).
I don't add an extra driver, but when I asked about it (can't remember if it was Alamo or Avis), they said it would be $5. They also may offer you an upgraded car class for a certain fee that may or may not be reasonable. I have never taken the upgraded, but I've been upgraded one class a few times for free when the class I booked was not available. They won't tell you that right away, so if they are pushing an upgrade that you have to pay for, it may be because they don't have the car you booked.
Once in a very great while, they will actually let you bid again right and away and tell you how much to bid to be assured of having it accepted. This has only happened to me once with cars and twice with hotels out of countless bids, but it does happen.
Barb
Visit the Platinum
Castaway Club at:
www.castawayclub.com