Since you said that actually money was a factor, can I recommend this which is an amazing place and a decent price:
http://rafikisafari.com/superlekker.html
Totally agree! We did the superlekker, which was one of the best parts of our trip to Costa Rica, though it seemed to me that that particular trip isn't always available and it's hard to know in advance if it will be. We also loved Lapa Rios on the Osa Peninsula, but that was more of a splurge.
I have a friend that works for Backroads, which is the company a PP mentioned, and they do some really incredible trips in many of the places mentioned.