I would say that $6250 per couple would be pretty reasonable when splitting the charter 4 ways. The way we handle the "common" items of the boat is really basic but works great. We keep a pen and pad in the salon throughout the trip. If a couple pays for something (mooring, ice, trash, groceries, etc) that is for the whole boat then it get written in your column. At the end of the trip we balance out who owes what and make one payment to even it out between everyone on board. We also do as Deepcut mentioned and pay for drinks/dinner ashore individually or just split the check evenly and call it a day.