Thanks to everyone for the Costa Rica travel tips! @kiraliz2, you were totally right about the cost of the car insurance. I was just happy to know what to expect, and the driving was fine.
We loved it and were glad to get to go to the beach. DS liked the water but wasn't sure about the sand. The people were really nice, and the food was good. DS (10 months) was 90% good on the flight. Next time maybe I'll take earplugs and thank-you candy for the people sitting around us on the plane.