The last time we bought a car, we were very fortunate to have a relative who could look up the local auction prices of cars--the auctions where only car dealers are allowed in.
After he gave us the information, I used it to haggle via email with a few local dealers. Hardly haggled: I emailed them asking if they had an XX car with XX miles or fewer and would be willing to sell it for $XX, including tax, tag, and title. Those who responded got my response in turn. We went to one of these dealers who had the best response (after setting up the appointment via email), we test drove the car, and we bought it for exactly $XX. While we were there, they tried getting us to pay $x more, but we said thanks but no thanks, and as we walked out they called us back and "gave" it to us for $XX. We paid by check.
I think you could reach your rock-bottom price via internet research (cars.com, edmunds.com, all those other websites) to find the best local price. I liked using a dealer b/c they all offered free carfax on each car, so we knew that none of them were flooded or otherwise undesirable.