We flew into International, and went to San Ignacio for a couple of days. Then on the way BACK, we drove to Muni, and flew to Ambergris. On the way back, we flew to Muni, taxied to International, and flew out of there.
For the money we saved for four of us, it was well worth it, and the cab ride was easy!
If you are looking for ease of transportation, take the flight over from intl. Our guests in Ambergris did this, and they said it was a very easy method.