Elf on the Shelf Scavenger Hunt

We're hosting a Christmas event in our town. Free for participants. Great for all ages - kids, teens, and adults. We will have a set number of elves hiding in local businesses. Participants will use the app to read the clues, find the elf, and enter a special code (that will be displayed on the elf's chest). After the participant has entered all the codes (depends on the number of elves - estimate 6-10 for this first year, with the capability of going up to 30 elves for future years), they will automatically be entered to win the grand prize of wrapped presents donated by local businesses. I'm looking for an app for participants to use to enter the codes, it will collect their personal information (especially email addresses so we can market to them later), and will be able to draw a random winner on our end of the app. We'll also need to be able to export the entries into an excel spreadsheet to upload the entries into our email contact list. We'll need the app to have the capability of only being open during a specific time frame for the event, and outside of the event time it will be closed on a landing page welcoming them to input their contact information to be notified of the winner / next year's event / etc. If we had the capability to do push notifications, that would be over the top amazing, but we can make do without if it's too timely/expensive. We'd need this app to be available on iPhones and Android phones.