I recently sold a K10D body here with about 4k clicks asking $525 + shipping - It was in immaculate shape. I think persoanlly between $500 - $550 seems fair to me. Then again a K10D is worth whatever someone is willing to pay
You can search the Markeplace (both for Sale and Sold ) threads to see what others are asking.
As for the lens I thnk I saw one in the Market Place for $300 , that one might have been a Pentax 18-250