If you’re willing to do a little work along the way, you can get paid to travel, instead of paying to travel. Some gigs will cover your transportation costs or your room and board; others will pay for your entire trip, or could even send you home with more money than you started with.
There is a response to the article from Sean Yang, one of the Airmule co-founders, in the comments. He argues that Airmule is entirely legal (not a point in dispute) and that Airmule is responsible for the contents of all the luggage carried by travelers. He also clarifies that they pay duties when required.