[11/13/2015 @ 5:28 PM] Price has increased to $246. Removing from the bookable deals list for now.
Southwest Airlines has round-trip flights from Houston (HOU) to San Jose, Costa Rica (SJO) for $198, NONSTOP. Flights from November to February.
You may want to book this as a one-way into Liberia (LIR) with a one-way out of San Jose (SJO). Doing it this way will get you closer to the coast and will allow you to see more of the country without needing to loop-back to your original airport. Total will end up being about $237 for both one-ways.
Click for more details and booking links Nonstop Flights: Houston to San Jose, Costa Rica $198 r/t – Southwest