For Dan88's edification, here are the results:
From 9/14/09 to 3/5/10, the bonus round has been played 125 times and won 52 times. The distribution is as follows:
$25,000: 15 solves/39 attempts
$30,000: 19/46
$35,000: 10/23
$40,000: 1/2
$45,000: 0/1
$50,000: 2/6
Cars: 5/8
Excluding the cars from consideration (as they have no fixed value, and if lost, no announced value in the recaps), we can compute the expected number of wins at each level by multiplying the probability of a bonus round win by the number of attempts at that prize level.
$25,000: 15 solves/16.22 expected
$30,000: 19 solves/19.14 expected
$35,000: 10 solves/9.57 expected
$40,000: 1 solve/0.83 expected
$45,000: 0 solves/0.42 expected
$50,000: 2 solves/2.5 expected
We therefore compute a chi-squared value of 0.66 on 6-1=5 degrees of freedom, which is not significant at the 5% level. Therefore, we fail to reject the null hypothesis that the bonus round difficulty is correlated with the prize amount.