Driving time from San Francisco to Samana city is about 2-1/2 hrs. Add 30 minutes more to Las Galeras although I have made it from LG to SFM in 2-1/2hrs. Santiago to Samana is about 3-1/2 hrs, to Las Galeras about 4 hrs. Santiago to Las Terrenas is also about 3-1/2 hrs
Local island airlines are Aerodomca and CaribAir with scheduled service from Santo Domingo to El Portillo in Las Terrenas. Charter service for Samana's Arroyo Barril airport is available via Aerodomca or Air Century from/to most on-island airports. They are listed in the Verizon DR phone book and have English speaking personnel on hand. It's better to deal with them direct as sometimes you may be able to share a charter flight with someone else.
Regarding costs versus taxis, two of us to fly from SD to Las Terrenas and then taxi to Las Galeras cost us $140usd to fly and then an additional $50usd for the taxi for a total of $190usd. Taxi fare from SD to Las Galeras is $175usd. Although only $15 cheaper, the taxi takes almost 5 hours whereas a taxi from downtown SD to La Isabela, then flight to el Portillo and then taxi to Las Galeras is a little over 2 hours total.
