For Surf City, you can take a bus on the main road just outside of the bus station in San Salvador. El Tunco is more touristic, if you prefer shops and all. Personally I prefer El Zonte. Fewer options, but good ones in terms of food. Way more options to spends sats. And more relaxed vibe, to my taste. But that was August, low season apparently. Ow yeah, along the coast itself, you can take a bus, Uber or perhaps rent a motor.