I think you are going to be stunned at the cost. To charter a overwater capable jet from South Florida to St Thomas I am going to estimate at 30,000 one way. I think that will be on the low side. You will probably need the heavy jet for over water. From STT it’s likely you will have to pay for the aircrafts return also if they can’t book a customer out of STT. That doubles the price.

Costs for chartering vary widely but expect to pay a minimum of about $1,500 per flight hour for a turboprop to $8,000 or more for a heavy jet.
G