Have you tried to align yourself with any Christian missions working in Central America? Lots of churches participate in supporting foreign missions. Our church supports missions in the San Blas Islands off the coast of Panama, we support mission work in Africa and China as well. I know that other churches in the United States do the same.
It should NOT be that difficult to combine your efforts with others working in the area already as there are LOTS of missionaries in Central America. I would inquire about other Christian relief efforts in the area, talk to them and see if there are others you can work with who have similar goals and existing contacts.
Our church does lots of remodel construction work in Panama, we work on programs there related to recovery from drug and alcohol addiction and we have supported medical missions in Africa and China as well. Most all of our supplies our donated, we even have businesses in the states who make regular donations for operating expenses for our missions.
Help is out there just don't stop looking for others who are led to do the same work as you. Foreign mission work is truly a great calling. You have my respect. Good luck and God bless.