Going with a US outfitter is the most efficient option, but is also expensive. A poor student with little money and a lot of time could try joining a research team as an unpaid helper. It has been years since I toyed with the idea, but when I did there were university groups of all sorts, from military-funded data collectors to environmentalists. University teams are often interested in saving limited grant money by paying fewer workers. This is a lot less glamorous option and one would need to do some work, but the ticket becomes free.