Crispis and Kenetrek - for the upper end of the boot market, if you are on a budget, watch camofire.com, they have both brands for sale pretty regularly and at a price cheaper (>$250) than any other site. They also take calls to the warehouse for orders if you need them now, and they have your size on hand.
As far as the temperature range you are looking at, it's going to be hard to find a non-insolated boot that is light enough to get you through the 80-90 degree temps, and still have enough room for the layers you will need for the sub-zero layers. With a 100 degree span, you are really looking at two pair of boots to do either end of the range well. JMO...
