Southwest has round-trip flights from Dallas (DAL) to Liberia, Costa Rica (LIR) for $386 with a connection. $178/$208 each-way. Flights January to May. Most availability is from March to May, other months are sparse. Weekends available. Origin/Destination reversible. No Holidays. Expect prices to fluctuate by about +/- $10.
Note: You can save up to an additional $150 if you book your Flight+Hotel together on Southwest Vacations and use the INT150 coupon-code at check-out.