We just got off the Magic (3/9) and on St Thomas we did Coki Beach for 2 1/2 hours (9 to 11:30) , then went to Magens Beach for 2 hours (12 to 2 p.m. approx) then were dropped off at the shopping area until 4 p.m. and it worked really well. Enjoyed the snorkeling at Coki beach and we got there early enough that it was not crowded at all...
boat to Coki 7.00 each
bus to Magens beach 4 to 6 each (sorry having a mind block)
Magens beach to shopping 7.00 each
shopping to boat 3.00 each
not cheap but it gave us a flexibility that the tours did not.
also the driver was incredibly reliable coming back exactly when he said he would
good luck