The airport in Manzanillo ZLO. There was some discussion on this in the FS Tamarindo thread. The only year round daily flights are through MEX on AM only (no LCCs)

There are seasonal flights to IAH, PHX and DFW one or two days a week. AS seems to have a year round flight from LAX a day or two a week.

I was looking to get from the east coast to there in May and the only flights I could find were through MEX any day of the week. In the end a pretty difficult place to get to from anywhere other than MEX as you would need to line up your schedule with the airline schedules to get any non stop flights from the states.