We did a 10 day trip on a Moorings 474 powercat. Fuel including generator use was just over $300 from what I remember. (You could search my past posts for a more accurate number). If you run the cat at a modest speed (we did 8-9 knots) it won't burn that much fuel at all. Considering that the distances in the BVI are quite short there's no real need to go roaring around at 20 knots even if the boat is capable of it. And a couple of benefits to the power cat include a much higher and larger flybridge (everyone will want to be up there trust me) and the lack of rigging for the sail. This makes the front deck more usable and mooring a lot easier. Our trip was your typical BVI loop including a visit to Anegada.