It looks like there is a lot of different charters available. I have only been to Costa Rica once and it was to Tamarindo for surfing. A beautiful country, I felt very safe there and the locals were phenomenal for information. Would like to go back some time. as I thoroughly enjoyed it more than Mexico. Found some links for you, I am sure you have done your research already and are looking for personal experience but ill throw down some links I came across.
Went a few years back. Will look and see if I can dig up the name of the place. Was a French captain, didn't do overly well but still a great day. Saw dolphins, a few 100 turtles and a manta ray jump out of the water. Using poppers caught jack and needle fish. Also got the one of the worst sun burs of my life.