When resorts are busiest, prices tend to be highest. If you can, avoid planning a trip during peak times (especially school holidays). Here's what the ski season tends to look like in terms of prices, conditions, and crowds.
Before Christmas. This earliest part of the season tends to be the cheapest--and the riskiest for planning. The first big storm may not happen in time, and conditions may not be right yet for man-made snow.
Holiday. Between Christmas and the beginning of January, the snow has usually arrived. Ski areas are typically at their most expensive and most crowded.
Value season. From early to mid-January, prices are in the mid range, snow coverage is usually good, and crowds are less intense than around Christmas.
Regular season. From mid-January to mid-March, snow coverage is dependably good--and prices are second only to those of the holiday week. Watch out for local school holidays, as these often bring a surge in slope population.
Spring skiing. Between mid-March and the end of April (or May in some higher altitudes), prices are almost as low as in the early season, and snow conditions are often good, especially on higher mountains that are still getting fresh snowfall.