As I mentioned, Delta flies into SJO airport and LIR airport, both from ATL. You can arrive one and return other (based on seats, of course). What sort of plans do you have in mind? You may want to split your 2 wks:
1) one interior--volcanoes, hot springs, hiking, coffee plantations, etc
2) one coastal--small beach towns or resort areas; there are plenty of either
Something for everyone.
Check the timing for weather issues, like rainy season, history, etc.
I might consider Panama for ease--happy to send you link for condo there (airline people). I've not stayed there but have been to Panama.