We just did this on Friday. Flying out of Grand Case on St. Barth Commuter air was 140 euros p/p round trip. We rented a car at Sixt for roughly 45 euros with insurance. They threw in a one hour parking pass for Gustavia. We did some window shopping in Gustavia (you could spend a pretty penny there) then drove around the island ending up at St. Jean for lunch at Nikki beach. We had a leisurely lunch and a bottle of wine. Total was 250 euros for 3 of us. We could have done lunch more cheaply by buying sandwiches etc in town and then taking them to Governors beach (which was really pretty). It was interesting that Nikki beach was more restaurant than beach club. There were no loungers on the beach or anything like that. Several of the beaches that we liked did not appear to have any concessions.

It wasn't a cheap day trip but something we've been wanting to do for a while. and we were glad we did it. Just the flight over in the little plane and landing on that runway is an experience. According to the tabloids, over New Year tons of celebrities were there. We didn't see any, but there were some massive yachts in the harbor.