Flying is probably the best way, but not the cheapest way and I think doing ferry is a good way to see the islands up close.very pretty. People have commented on the rough seas they experiencd ..but when we went over we had some wind but the seas were not that bad. We did take nondrowsy Dramamine .
There are several to choose from with $70 being the cheapest round-trip. We chose the voyager because it gave more time on the island departed from Marigot at 850 and arrived an hour later and left Saint Barts at 515pm. The edge is another feery that leaves out of Simpson Bay. I think the third is great Bay express? Just Google all those names and she's the one you want if that's the way you want to go . Hope this helps.