Well my best bet would be:
1. Create a landing page
2. Let people fill in there details, name, surname, e-mail etc.
3. Get a little checkbox letting them agree to receive newsletters
4. Let them press submit
5. Thank you for participating! Please confirm your submission by completing the survey below. Once completed you will enter the lucky prize draw ( or something like that ).
This way you can build a e-mail list and people will complete surveys to "complete" their sign-up for the prize.
Either way if you get 10.000 people who will do this and only 10 will complete the survey you can even cash in after with the e-mail list youve build.