Travel for cheap? South America, Africa, China?

With that amount of time to plan, I am positive you can get funding of some sort. Especially if you want to plan to do a study abroad or international internship at the end of your undergraduate. If you are a talented student you can definitely get a scholarship or a spot working on research with a faculty member.

Based on the substance within your question, you seem to be very focused and ambitious and are likely to pull off a great trip.

Good site to get you directed:
http://www.ngoabroad.com/