There's an Arc'teryx factory sale in Vancouver on 'til the end of the year. Their gear is usually way out of my budget, but they had three models of pants marked down to $199 from $650. Picked up a pair to replace my bottom of the line Burton pants.
Personally I will only buy pants 20K or higher, although 15K+ is probably sufficient. I definitely wouldn't go any lower than that unless you plan to buy new pants every season, use waterproofing wash/spray regularly, and don't do much hiking/sitting/falling.
I wear the 686 LTD Destructed Denim and have never even been close to wet this season on a full day of riding. 15k waterproof, 10k breathability. Maybe in wet spring conditions that could change but every time I go in the lodge it just pours off my gear and dries in a hurry.