One other thought. Be sure you really think this through. People will try to scam you.
For example, you might want to state that the reward will be paid in three monthly chunks starting thirty days after the contest closes.
Why? Someone can easily put $3,000 on a credit card to win and then reverse the charges on you five days later. The installment payment approach will not prevent all fraud, it's just one idea to at least filter out some of it. Check with credit card companies/PayPal before you do anything.
It might be intelligent to install other limits as well. Again, take your time to think it through.
