At the small park on the main stip ( Calle Duarte ) in front of Hotel Don Paco.
50 pesos, It will take you to a small bus depot there you get on a second bus.
Its runs pretty frequent.
Its gone up to 60 pesos now (i just returned). Never seen a guagua on Duarte itself...but i catch it anywhere on the street that runs parallel to Duarte in BC (calle san rafael). I catch it right across the small church that is across from "central park"
The first guagua is free and then you pay when your transfer at the small Depot on the highway. I usually try to grab a seat up front and let the driver know that i want to get off at parque indepencia.
Now the hard part (for me) is trying to figure out which guagua to catch in S.D. to get me back to the bus terminal THERE to catch the guagua back to B.C. I've done it once with a friend..and i know the ave (ave mella?) that it runs on...i just dont know which one to take so i end up taking a taxi (200 pesos) to the station in S.D. DO make sure that you catch the guagua that says Express on the way back (it still makes some stops near and in Andreas...but the other one makes many many more stops).
One question I have is... when DOES the last guagua run from SD to BC? Some people tell me 11pm some tell me 9 PM.
@ the OP. I think i am making this sound more difficult than it is. I find getting from BC to SD very easy...just a bit more confusing on the way back.
One last thing. Its always good to know and have the exact fare with you. And the guaguas (busses) at either depot depart when the bus is full.