Assuming you're clearing into the BVI on a charter boat:

* For both a USVI- and BVI-based charter boat, there are identical fees for the BVI Environmental & Levy that went in effect on Sept 1st ($10 per-person) and the BVI Departure Tax ($20 per-person).

* The BVI National Park permit for a USVI-based boat is $50/week (up to 4 persons), $70/week (5-6 persons), $90/week (7-8), $110/week (9-10). This is twice the rate as for a BVI boat, which works out to ~$1/day more per-person for a USVI-based boat.

* The BVI Cruising Tax was increased for both USVI and BVI based charter boats effective Aug 1st. The per-person daily rate is $16 for a USVI boat and $6 for a BVI boat.

* For a USVI based boat, there are vessel fees for Harbor Dues ($10), Customs & Immigrations Services fee ($5~$20, non-overtime), and Boat License ($15~$45). There seem to be at the discretion of the officer on duty.

* Clearing out of the BVI's, there's a ~75 cent fee (per vessel) for stamping some forms.

So all depending on crew size, you're looking at an extra $11~$13/day per-person for a USVI-boat while you're in the BVIs. On a 7-day charter originating in the USVI, most will likely only spend 5 days in the BVIs so an incremental $55~$65 per-person in BVI fees. On the other hand, you'll easily spend 2x-3x these in roundtrip taxi and ferry fees if you travel to the BVI via STT (not to mention the associated travel time when you could be sailing instead). You'll also have higher provisioning costs in the BVI vs St Thomas.

If you're clearing into the BVI on a private vessel, the above BVI Departure Tax, BVI Cruising Tax, and Boat License are not charged. There's an annual tonnage fee of about ~$50 for your first entry into the BVI that year.

Returning to the USVI, the only fees I've ever been charged are for the following:
* C&I Holiday overtime fee (~$25 per vessel)
* Dockage fee for tying up to the C&I dock at St John (~$20 as I recall from 10 years ago)