Hi! I’m a senior, and here are the programs that I looked into last year:
Vernon L. Smith High School Workshop in Experimental Economics (http://www.chapman.edu/research-and-institutions/economic-science-institute/conferences-and-workshops/high-school-workshop.aspx)
Hosted at Chapman University in Orange, CA. It used to be that they had travel reimbursement for out-of-state participants, but it seems that in 2016 they don’t anymore. It’s a week long, and free. Everyone earns roughly $150. I went to this and it was really fun! They provide meals as well.
Economics for Leaders (http://www.fte.org/student-programs/economics-for-leaders-program/)
Hosted at various universities across the country; some spots fill up faster than others. There are scholarships available, but are limited by state or have a deadline. It’s a week long, and costs approx. $1000. I was accepted but didn’t go, so I can’t attest to the quality of this program.
Seminars by the Foundation for Economic Education (http://fee.org/students/)
Hosted at various locations. This 3-4 day long seminar is free, but you must pay for travel costs. I vaguely recall possible scholarships but I can’t find anything, so I might be wrong. Some seminars are more popular than others. I would really encourage you to apply to this one, since the application “essay” is only 100 words and you will receive and acceptance/rejection letter soon after (for me I think it was 3 days). I also didn’t go to this one, but from what I read on CC, the seminars all have a very libertarian slant. However, discussion and debate seem to be highly encouraged.
Not exactly the same, but this program is sponsored by the same organization as the first program I mentioned. The focus is different as well.
Virtual World Experiments in Experimental Economics (http://www.kevinmccabe.net/ifree/)
Hosted on the Arlington, VA campus of George Mason University. The program is free, and has rolling admissions, but very limited spots. The program’s focus is on Neuroeconomics, and students who have taken AP CompSci are prioritized. Participants earn money, and meals are provided.
Honestly, it’s really hard to find econ-related programs. You’d have better luck finding a business program, supposedly the LEAD program at Wharton (UPenn) is good, but probably expensive. As for other activities, such as research assistant: that’s really up to your local university, but it doesn’t hurt to call, email, or visit to express interest. This would probably be harder, but you could try to intern at a think tank.
Good luck! Since everyone takes econ in some capacity, it’s really hard to show passion, but there are options out there. Wow, this comment was longer than some of my supplement essays