If you're a student 13 years or older and you can't pony up the $1,599 for the standard registration fee for WWDC, fret not - Apple is once again offering student scholarships. This year they've set aside up to 150 tickets for aspiring student developers who want to come. (Getting to San Francisco and finding a place to stay is still up to you, though.)
To apply, you have to meet the eligibility requirements, so make sure to visit Apple's web site to make sure. Then you have to create an app that "should highlight development projects you’ve worked on, your educational and professional background, technical skills, and interests." The app can run on either iOS or OS X.
Apple will accept submissions from April 29th to May 2nd, so you don't have much time to get your app together. So put your nose to the grindstone and get going!