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.
17 Korua Apollo . 17 Nitro Treehugger . 17 Lib x Lost Mayhem Short Fat . 17 Jones Storm Chaser . 16 Never Summer Swift
17 Burton Malavita Wing . 16 Burton Genesis X
16 Flow Talon