The Dolphin Water Taxi option (from STT to EIS) costs are $229pp inbound and $169 outbound. Inbound is via air. Outbound via boat and they'll pick you up at your charter base. That said, I totally agree with what someone said earlier on this forum, Jason I think, why torture yourself with the STT airport? SJU is much nicer, not crowed, and all-in the total cost to get to EIS is not much different. Here is the link to the Dolphin site:

https://www.dolphinshuttle.com/covid-19-restrictions