You aren't able to rent snorkel gear but kayaks are about 20$ for 4 hours if I remember correctly. It would be quite a swim to the sandbar if you planned to do that (about a mile and half) so kayaks are pretty much required. Make sure to go on the right day as well. Plan for low tide.
No snorkel gear there but there is a few places around marathon you can rent
They rent both
Yes i used my own gear, not sure if they rent snorkel gear but they do have kyaks and paddle board rental for reasonable rates
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