Here's an option / purchase deal memo for a book that might be adaptable for your needs:
http://www.cypressfilms.com/book_option_author.htmlHere's an excellent book on the subject of entertainment deals:
http://search.barnesandnoble.com/Hollywood-Dealmaking/Dina-Appleton/e/9781581152289/If you're near a decent bookstore like Barnes & Noble, I'd run in and see if they have a copy and see if it works for you.
Because there's no "standard" screenwriting deal memo, there all created as needed by entertainment attorneys. This is especially true if there are back-end points involved. The book above is about as close as it gets.