At DEN you can get great deals through Priceline on a car rental (just not SUVs) for around $20/day or less then either stay in DEN and drive up to the mountains (like the locals!) -- about 1.5 to 2 hours drive -- or stay in Frisco/Dillon/Silverthorne. Some of the hotels here are part of Hotwire/Priceline and good deals can be had on those as well.

As the rjque mentioned, for ski-in / ski-out lodging you will pay unless reserved far in advance. Check the websites of the major resorts for mid-week deals and don't be afraid to look at "secondary" resorts that are not the typical tourist destinations (Crested Butte, Winter Park/Mary Jane, Copper, Loveland, Steamboat, Eldora, etc.). Obviously Heavenly, Breckenridge, Vail, Aspen, Keystone and other heavily market resorts will be charging up the nose.