To find out the contestant's balance in prize money after answering six questions wrong, we can calculate the total loss from those wrong answers.
The contestant loses $12.50 for each wrong answer, and if they answered six questions wrong, the total loss would be:
\[ \text{Total Loss} = \text{Number of Wrong Answers} \times \text{Loss per Wrong Answer} \]
\[ \text{Total Loss} = 6 \times 12.50 = 75 \]
Since the contestant has answered all questions wrong, their balance in prize money would be a negative amount:
\[ \text{Balance} = -75 \]
So, the balance in prize money is -75, which corresponds to option D: -$75.