You don't "plan" a last minute ski trip
Hmm. If you are worried about condos, I'm wondering about your priorities.
IMO the only reason to do last minute ski trips is to be where its dumping when its dumping. However, those powder days come at a price--you may not be able to get the good condo (or you will pay more for it) and you probably will pay higher airfare if you are going to fly. But who cares if you're skiing hip deep blower right?
The deal with last minute trips is you have to be flexible enough to roll with whatever is available (or not available). You don't really plan last minute trips because you can't. You either make the best of what you get at your destination, you go somewhere else, or you postpone your trip and hope for a better draw the next time. If you can't be flexible, and you still want to book last minute, then you have to be ok with the fact that your trip might not happen.
You can't really expect to get a good deal on lodging and airfare at a big name resort at the height of the season when you book last minute. When demand is at its highest you will pay a premium. To work around that, you can:
a) Go at a time when demand is less (i.e. late April in Whistler Blackcomb--still lots of snow & screaming deals because nobody is up there).
b) Don't stay on the mountain (i.e. the town of Jackson, Reno, or SLC). Its far less expensive to stay in town than it is to stay slopeside & you can almost always find a bed (regardless of season).
c) Go somewhere else where the demand is lower and the deals are better.
d) Drive instead of fly. Its way more fun and way more flexible. You'd probably never fly to Missoula to ski Snowbowl (which is too bad), but if you were passing through, you'd probably stop. Less practical if you live back east (then again, you can fly to Denver or SLC and rent), but IMO driving trips are the best way to travel last minute. Just get in the car and go--bring your cell phone to find lodging while you are driving & point the car in a different direction if it doesn't work out.