AN,
Pick the one you like best and negotiate the best deal you can. If you arent satisfied with the price move on. What happens when you buy a car and the rebate goes up next week or you buy a TV and it goes on sale next week. Its all part of life and you can only control so much.

BTW What you are suggesting is a “reverse auction” which was attempted in numerous internet models during the hey day. To my knowledge none of them were terribly successful.