My daughter and Mon just did the dolphin encounter at Chakkannab. THey booked through the internet and was a little under $300 for the both of them. We could watch from a distance (200 yds). If you wanted to watch closer it was another $5, but you may not take any photos.
You must wear a life jacket and if you a a novice swimmer you can use a kick board to get out for the fin swim. A staffer will assist you in swimming out if needed. I would suggest booking early in the day. We had a 10am time and there was only a few groups. THeir group had 7 people. Later in the day the groups were larger in size and more numerous around the lagoon when we left at 2pm.
It was an excellent experience. They take pics and make a video at the end for $80. Each Pic is $20 if you dont take the package. We lounged around the beach and snorkeled for the rest of the afternoon. The place was spotless, including the restrooms.