That's just before Christmas and during holiday season. You probably won't find anything cheap. Prices around Christmas break are significantly more than other times of the season. VRBO is the place to start. In general, the further away you stay from the mountain, the less expensive. Happy hunting.
I've rented from this company and they were very good to deal with. They had the best ski in/ski out deals at Copper. The condo we stayed in was a great deal, probably mostly because it was a little dated (the pictures depicted it accurately), but it was comfortable. Our 3 bedroom was only $600 during spring break this year.