If you are talkin about scuba..it depends on your time slot as well as the area from where u drive in. early morning slots are approx 4000 RS and deep sea dive is around 6500. I wont suggest doing sea walk there or snorkeling.. it's better you go for scuba!!
That depends on what water activities you plan to do. The top water activities in Havelock are priced liek:Scuba Diving: ₹3,500 to ₹4,500 per person
Basic Guided Snorkeling: ₹800 to ₹1,500/- pp Sea Walking for (15 mins): ₹3,000 to ₹4,500/- pp