Air Santo Domingo
In late July, I hopped around a bit on ASD. I also used another small airline whose name escapes me to get from Las Terrenas to SD. In that case I used a travel agent in Las Terrenas to buy the ticket.
As for ASD, I flew from Punta Cana to POP--I bought the ticket in an office off the airport the day before the flight. No problem at all.
In both cases, I was pleased with on-time performance. I must say that there is very little chance that the two young pilots have any desire to meet their maker any time soon, so my feeling is that you will be safe.
There is nothing so exciting as flying at fairly low altitudes over this beautiful country--carry a bottle of water because it can get fairly hot at times before the air conditioning kicks in.
Abe