I have shot a nikon D70 in all kinds of weather, including rain and snow and it works same as new. I see no reason why the newer D90 could not take this same abuse for less than $1k. Another option is to go to the used market for a semi-pro nikon or canon body. The nikon D200 is around $800 used and is an upgrade to the D90 in the abuse category. I'm sure there is a canon equivalent. Going up to $1400 or so gets a used nikon D2x which is full pro, 12MP, and is about as tough as a hammer. look on ebay, keh.com and there might be other places. If going used, make sure to ask how many pictures the camera has taken. I think its in the EXIF data.
That pentax has a nice magnesium frame, but the canon and nikon camera systems are more robust.