Forget about PC in December. You can stay in Sandy and ski Alta/Snowbird with pretty good confidence in mid-December. Orbitz shows fox rentals at $12/day. It is insane not to get a car. If it is snowing and you can't get up the canyon, just get to the bus stop at the bottom early enough to get an easy ride up. I'm sure you'll be first in the lift line anyway.
I skied there the last two years 2nd weekend in December and the conditions and amt of open terrain were quite good both years. But last year I was saved by 4 or more feet of snow starting the evening before i arrived. Skiing was Great! The year before I caught the rope drop at Mineral Basin. You can do this trip cheap and get the best skiing and greatest snow on earth at the same time, and no crowds whatsoever. Also, it is just a great feeling to be on the hill in December and a super way to start the winter.
You can still ski the first half day for Free at PC(if they offer it then). Also, don't know where you are coming from, but if your flight leaves leaves after 2pm, you can easily ski 1/2 day. Stay 4 nts, get 5 days of skiing in, that should be plenty. I have at least 2 dozen 3 nts trip in at SLC. I see Delta from Orlando has those magic early morning and late afternoon returns that should do you good.