You have not mentioned the locatoon.

for the local and foreign , 10 people for local 2050 rs , life jacket with 30 minute boat ride ,,,,, 6 people for 4000 rs with life jacket with 30 minute boat ride ,,

There a various sizes of boat with different passenger numbers for each trip. It's best to ask a few boat operators and negotiate the price. If your party is small , ask others in your hotel to share with you.

Tide was strong in March when we were there. Suggest you look also at the websites for weather and advice for the region. Always take local advice before going into the water for anything.

Once the sun is up, they come around. The locals have been feeding them, so the visit is kind of habitual. Them sill being wild animals, the visits are not guaranteed. While you wait walk down the beach, past the Chaaya tranz, towards Hikkaduwa town, and you will get to the "Swimming Spot" where you can do shallow skin diving where herds of fish and beautiful coral formations are guaranteed. Simply, visiting there will not be a waste at all. Travel safe...!

Well I think as Sri Lanka doesn't have much of seasonal effects and the water is warmer throughout the year, the turtles too should be there. We saw a big one when we went there and there's this local person who comes and let tourists feed the turtle and also take pictures with him.. then he will also ask money (That's so pathetic because he doesn't own the turtle) few bucks would do. And swimming along with them, I think you have to be lucky for that!!! Have fun ...