There is a ferry from West End to JVD. Add on round trip taxi to West End.

I doubt a water taxi both ways for seven (two round-trips for boat operator) will be much cheaper than a private day excursion. All commercial (for hire) boats need trade licenses, insurance, etc., so their costs are high. They also expect a tip.

If cost is your driver, buy round-trip ferry tickets to VG and rent a car.