I visited Myakka on a cool, cloudy day in late December. This weather is not as conducive to alligators sunning themselves, but we were still able to see a lot of them. Cost of admission to the park is $6 for out of state residents. The boat ride costs $12 but was worth it - the driver is very knowledgeable about the birds and alligators, and knows where to find the alligators if they don't want to be seen. We saw a bald eagle, osprey, herons, roseate spoonbills, lots of other birds, and alligators! The boat rides sell out quickly on busy days so it would be good to buy your ticket several hours in advance and then do some exploring.
If you are interested in a history of the park and area, go on the tram ride instead of the boat ride. You will learn a lot of history but won't see much wildlife.
Another good place to see alligators is at the man-made dam at the end of the large parking lot at the end of the road near the boat launch/gift shop area. Head directly across the road from where you buy tickets for the rides, go behind the trading post (another small gift shop where you can rent bikes), and continue through the trees until you see a path develop. It's a short walk to the dam. Even though it is clearly marked to stay off, there were a lot of people there watching the alligators and birds. A great place to get some pictures.
We also went to the bird watching area, which is a long boardwalk out to the edge of the river. Take some binoculars and you can see a long ways, and lots of water birds.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.