Here's my fuel consumption on my Saba 50 for a recent 10 day trip in the BVIs (I excluded any motoring time to/from STT to the BVIs).

We had good sailing winds but still managed to put about 15 hrs on each Volvo D2-75 engine. We burn ~1.3 gal/hr per engine at 2000 rpm cruise. This gives us 7.4 kts with both engines running. So I estimate 39 gallons total on the engines. The Helia 44 has a smaller engine, but fuel burn will be comparable if you push the rpms to get to this speed.

We ran the generator for 60 hrs, or average of 6.7 hrs/day while off the dock. We have an icemaker and you can figure on at least 2 hrs of charging time per day just to replenish the amps used by the icemaker. We only ran the generator once overnight. With ~50% of the AC units on and some watermaker load, it burns about 0.5 gal/hr on average. So I estimate 30 gallons on the generator.

Total fuel burn ~70 gallons. On March 6th, diesel was $4.02/gal at Crown Bay Marina, St Thomas, and had been trending upwards since last year.

$300 is probably a reasonable ball park estimate depending on BVI fuel prices. You can easily double the generator fuel estimate if you run the AC all night long, and double the engine fuel estimate if you're skunked with no wind.