California Naturalist Program: UC-Davis: $300

California runs a certified naturalist program that looks really good. These seem to be online right now. The Catalina Island program costs $240 and the UC-Davis credits seem like they are in the neighborhood of $85. I think that $300 is pretty good to become a certified naturalist.

http://calnat.ucanr.edu/Take_a_class/
https://www.catalinaconservancy.org/index.php?s=about&p=naturalist_training_program
http://cecentralsierra.ucanr.edu/files/194197.pdf