Travelling in Cantral America

Hey - this is the first time I've set up or used a blog... thank you for reading it!

I'm doing a diving course in Honduras in July and August and am required by visa restrictions to have onward travel booked before I enter the country (Guatemala is within the same restriction so I cannot leave Honduras to go directly there). I am keen to travel Central and South America; Costa Rica, Guatemala, Peru, Brazil and Chile all appeal. I have never travelled like this before and will be going alone and on a tight budget. Flights around the region are very expensive so I'm seeking advice from people who have been to these countries as to how they would suggest I get out of Honduras, making my way slowly south, in a safe and inexpensive way... I have no time constraints whatsoever and would like to see the countries I'm passing through so bus/ train would suit.... I am struggling to find much useful info online.... any ideas anyone?! Greatly recieved! Kat