Note: the last time I went to Northstar in 2011 a day ticket was $70.
The day ticket price at Whitefish Mountain Resort where I ski is $78 at full price. costco sells tickets for $50 and you can get discounts in many other ways too. My Pass at WFMR is $685 and I ski there about 40 times per year. So good deal for me at about $17/ski.