I agree with KS. US dollars are accepted almost every where, Prisca's Ice Crean is the only exception I know of for sure. Do expect most of your change to be in Guilders and watch the value of the coins. I still have trouble dealing 3($1.70 US) and 5 (=$2.83 US)Guilder coins, just can't get use to using the larger value coins (my problem, not theirs). I find the food prices about the same as here in Raleigh. You can get a good $10 pizza or spend $35 or more on a big steak. Some of the local "snacks" have some good deals. The grocerie stores are a little higher than here, maybe by 10% or so. The exchange rate for the USD is about 1.77 (it varies a little between banks and stores). That works out to about $0.565 = 1 Guilder. I usally just figure 50 cents to the Guilder for easy math.
We are returning in early June, 2 diving couples 40-50ish, come join us if you like. We would be happy to show you around the island and can always use another dive buddy.