Hi Nitin, You can visit Alibaug beach which is around 150 kms from Pune. There are several beaches near alibaug. To name some, Nagaon Beach (10 kms from alibaug), Revdanda Beach (18 kms from alibaug), Kashid Beach (35 kms from alibaug). You can even enjoy water sports at Nagaon beach at very reasonable rates. Hope that helps!!!
Nearest are Diveagar, Shrivardhan and Harihareshwar. But if you are planning to go the distance, you should consider Ganpatipule or Tarkarli(Malvan). Personally, I liked these 2 beaches much more in terms of cleanliness of water and activities that can be done there.