The more places you can pay out the better. Knock the top prize back to $1500 and go down from there with placing further out. Even if you only pay five more places with that $500 it will attract more people. In a 50 boat field, making top 15 should at least mean going home breaking even on entry fees. You still lost money on gas, baits....
This is going to attract some people who are not as confident. The less places you pay out, guys start thinking how good they really are, especially at $100.