Pants are one of the most essential items for riding ski or snowboard.
There are different cuts and styles, and more or less features in a pants which makes the main price difference. The higher the water column and breathability is, the more expencive the pants can get, and the dryer and warmer you are whilst riding in harsh conditions.
The water column starts at 3000mm and goes up to 25000 with Goretex improved fabrics and materials. Same as the breathability in the pants.
To get the warmest and best feeling, you have to wear functional underwear underneath your pants and jackets.