Dropr is free to join and use a limited amount of 20-50 uploads (depends who invited you :)). After joining you get +1 new upload every week.
If you need more uploads or want to support the project, you can upgrade to a "GURU" account: https://dropr.com/guru which gives you a lot of additional design functionality and unlimited uploads. Upgrading costs $99 per year or $9.99 per month. The price can get lower as we run various promotions, check Twitter and your friends for a promo code!
There are also other ways to get free uploads, like referring Dropr to your friends: http://dropr.com/network/invite
See also: What is GURU?