Prices may have changed a bit but last time we were there (2022) it was $12.00pp round trip to Maho and back. Go to the taxi stand (easy to find or just ask someone) and they'll be taxi vans waiting to go that seat usually 10-12 people. Purchase your roundtrip ticket and they will put a colored wrist tag on you.
When you're ready to leave just go out front of the Sunset Bar (which is where you'll be dropped off originally) and you'll be directed to one of the returning taxi vans.
We opt to have them drop us off in town for some shopping and then we take the water taxi ($) back to the dock area.
We've done this over the years many times. You absolutely don't need an excursion for this as it's so easy to do.
Enjoy !!