Re. credit, one can do a random Thrifty car rental for $20ish and revalidate the miles.
Other gateway info:
TACA flies from YYZ, SFO, LAX, DFW, IAH, MSY, ORD, IAD, JFK, and BOS
TACA route map here:
http://www.taca.com/eng/iabo/iaboroumap.asp#
COPA flies from LAX, MIA, and MCO to PTY
Others are pretty much covered above.