San Juan Del Sur is very walkable. I say the best way to get around here is on foot. Secondly, many locals and foreigners in San Juan Del Sur use motorcycles as their primary means of transportation.
When it comes to public transportation, you can hire or catch a "colectivo" taxi. The term “colectivo” means “shared,” so basically, if you're on a street corner within San Juan Del Sur, you can hail one of these taxis and hop in for a ride. There may already be people in the taxi or there may not. If not, then it's likely that you will pick up a couple of passengers before you get to your destination. The cost for a colectivo ride is 20 Córdobas (US $0.65) per person and the taxi will take you anywhere in San Juan Del Sur. The cost would be 20 Córdobas (US $0.65) if you're at the grocery store with a load of groceries and you need to go to your home, you are going to the city center of San Juan Del Sur, or on the outskirts of town.
Sometimes these colectivo taxis will go outside of San Juan Del Sur proper, especially in one neighborhood called Las Delicias. This neighborhood is about a five-minute drive out of San Juan Del Sur and these colectivo taxis drive up and down that road daily and at night as well. It's still the same price, 20 Córdobas (US $0.65) per person.
There's another neighborhood that is on the way out of town towards the city of Rivas where you can also get a colectivo taxi along that bit of road for 20 Córdobas (US $0.65) as well.
If you want to go to the city of Rivas for shopping, to go see a baseball game, or for an appointment, you can get a colectivo taxi to Rivas for 50 Córdobas ($1.65) per person. That's about a 30-minute drive.
(VW bus that doubles at a shave ice stand, San Juan del Sur, Nicaragua, pictured.)