Endura's MT500 Spray Baggy Shorts are the answer to wet-weather off-roading. Waterproof, seam-taped rear panels keep your rear end dry and are mated to a 4-way stretch Cordura front for stellar comfort. For dialing in even more comfort there are zip mesh thigh vents and an adjustable waistband with integral belt. You also get zippered front pockets, hem adjusters, and reflective details for enhanced visibility.  Retails for $130.  Size medium, large, extra large and extra extra large.  
Discounts on multiple purchases.

Shipping is $7 in the US.