It's not a bad ride anymore, as the Western, Hummingbird and Southern highways are all now paved, except for about 5 miles of the Southern. Just bus to Belmopan and catch a James Line bus heading to PG. It's about a 5 1/2 to 6 hour ride from San Ignacio to PG, depending on connections. Think there's one James Line express bus from Belmopan and seven or eight locals.
If you want to fly, you'll have to go back to Belize City. A bus will take 2 1/2 hours or so to Belize City. A shuttle van will be a little faster, but cost about 10 times as much (the bus is only US$4 or $5.) Fly from the municipal airport, not from the international airport (BZE), and you'll save a few bucks. No flights from San Ignacio or Belmopan. Flights take about an hour from Belize City to PG.
All in all you'll only save about 2 or 3 hours if you fly.
Only catch about busing it is that the temporary Kendal bridge over the Sittee River just south of Maya Centre is sometimes flooded after heavy rains. That will either stop you or slow you down if they're transporting people by boat across the river.
--Lan Sluder
http://www.belizefirst.com