We did this on our own with Nauti Nymph. I seem to recall a past topic though where I think it was mentioned they may not allow this without hiring a captain now?
For 4 of us, cost was reasonable enough and we did a loop around tortola, stopped at the baths and caves. I'd probably skip the loop if we were to do it again and go right to the baths, then cooper for lunch maybe with a stop at the indians. Should be possible to fit that all in.