There's some potential for gamification here. Here's a Gumroad URL which, when paid for, unlocks some kind of challenge that you must solve in order to find a new Gumroad URL. Which unlocks another challenge that leads to another Gumroad URL, continuing for n steps until you unlock the final reward. Each step costs less than a dollar.

How would this have played out if eg. Dropbox had run their challenge on top of Gumroad?