Alibaug town is walkable but the beaches are spread out — Kihim is 10 km north, Akshi 5 km south, Nagaon 9 km south. Auto-rickshaws are plentiful and metered (officially); shared six-seaters run on fixed routes between the villages and are very cheap.
Renting a scooter for the day is the easiest way to see several beaches. A few places near the ST bus stand and Mandwa jetty hire them out by the day.