My brother and I went to Montezuma to do some surfing and we ended up at renting some boards from the folks at Proyecto Montezuma. Their shop is located right on the main street at the lower part of town next to the beach and is easy to find. Not only did they hook us up with the right gear, they also drove us to the best surf break given the conditions. We were able to hang out with them and learn about other good areas to surf. They really made our experience, as we new nothing about the area.
We had previously spent some time in Santa Teresa, but as a beginner surfer I found the beach break extremely challenging. Bill and Kerri brought us to an awesome left handed point break that was much easier to paddle out and catch waves. Would definitely suggest hooking up with these people if you want to learn how to surf in Costa Rica.
They also run a non-profit organization that certifies volunteers to teach English so you can learn to surf, help the local community and become TEFL certified all at the same time. Highly recommended, thanks a lot!