I rent cars with Priceline all the time. Using PL saves me an enormous amount of money on daily rentals for business. The best way to find out the going rate is to look at the histories posted on biddingfortravel.c__.
(Note that you probably do not want to register and post it as a question, because the moderator there is rather a martinet, and very hard to deal with. Just read others' posts and the Rental Car FAQ, and you'll see what the going rate is.)
However, Orlando has some of the best rental deals in the entire country, and I don't PL there as a general rule; you can do about as well using mousesaver codes most of the time, and the incidental terms are better when you rent directly. (Emerald Aisle, QS, etc., + FF miles.)