Um, you just mentioned "sponsors"... is there a catch?

Not at all. To participate in Sampler all you need is yourself and time.  There are no fees and no requirements to fundraise.  However, asking people from your congregation, your grandparents, your uncle's trucking company, etc. to help support you in this program is a way of inviting others to participate in Sampler too.  The service projects, discernment, traveling, and classes that make up Sampler take a lot of energy and time, and this is one way that other people you know can support you in that commitment.   It also helps offset time spent away from working a summer job.