The new generation of Crux AK-37 and 47 are waterproof. Very well regarded for their purpose (mountaineering), would make a great daypack if it fits your frame. Also within your price range.
I have two HMG packs that I love. The porter can handle +-50 lbs, the windrider can do 35ish with aplomb. They are all inherently waterproof; you may have to re-tape seams from time to time. Not built for brush beating abuse, but crazy light for what they can haul.
