couple of days late:
A professor was giving a big test one day to his students. He handed out all of the tests and went back to his desk to wait. Once the test was over the students all handed the tests back in. The professor noticed that one of the students had attached a $100 bill to his test with a note saying "A dollar per point." The next class the professor handed the graded tests back out. This student got back his test, his test grade, and $64 change.
(I had a student like that in my freshman calculus class. Never offered me money, but he had a strong 30% average on tests. Might have helped if he ever showed up for class and not just the tests.)