Hi Sharon!
I took your original question. :-)
You just need park admission to Typhoon Lagoon to be able to experience Shark Reef. There's no extra cost beyond your admission ticket.
If all you were interested in is going to Typhoon Lagoon alone, you'd actually save money just buying the ticket at the entrance gate (currently at $48.98 for adults).
If you're going to visit some of the Theme Parks, and get the Magic Your Way ticket, you'd pay more getting the Water Parks & More option, unless you were planning to make multiple visits to the Water Parks. To add the Water Parks option on a 1 day Magic Your Way pass (for an adult), is an additional $54. So you can see how purchasing at gate saves you a few dollars.
Good luck, and have a "splash" of a time!