Pack enough food/formula/diapers to just get through the plane trip, and then simply buy what you need on the other end. While it is true that resort destinations charge a bit more for formula, my experience, its not astronomical. Besides, if you check your liquid formula, be prepared to pay extra for the added weight if you are over the limit. Another cost.
Even if you use the liquid brands, you might wish to consider powder formula for trips, as liquids can be much more costly. On that note,
Otherwise your bag gets really heavy.