Does anyone know where the cheapest place for flights within South and Central America can be found? I'm looking to fly between Costa Rica and Argentina, but the cheapest I can find it ?00, and that seems quite expensive.

Try looking on Opodo, I was looking for some flights to Europe and did a quick search for you and it came up with about ?60.

Thank you I shall have a look-ski!

Buy the flights when you get there - or phone a local travel agent in country i'm pretty sure you can get them for less than that or try booking directly with local airlines like Avianca and Taca - I think they operate more like easyjet and ryanair as in you need to book directly with them.