Hello fellow Mid Westerner. It is possible to do it for a lot less than $100 per person. I just came back from there with a third person (8yr old) and we spent $100 per day for all three and didn't feel deprived. Pretend like you're in college again. There's nothing wrong with having drinks in your room, especially when you're looking out at the beautiful sea and it's 80 degrees. I brought down some wine, fearing I wouldn't find good ones in my price range, but I later learned it's possible. Also, take some days to do nothing except lay on a hammock and read to make up for the $200 excursion days. Afterall, it's the weather - the sun - the sand and snorkeling plus some scenic adventure you're after. (You can drink lots of beer in Nebraska, but you can't get a tan). On AC, for a mid-priced but VERY good dinnner, (our fanciest, besides new year's at Taste of Thailand) we went to El Patio. Sometimes we had appetisers as our entrees. You'll figure out how to do it. Also there's no reason you can't walk nearly every where. Even my whiny 8 year old could manage a walk from putt putt to the end of town. We only took a taxi once while there.
I echo the don't worry about the clothes business. Long sleeve coverups are good ideas as are multiple hats and bathing suits. We managed to get home with very little burned skin. (Don't scrimp on the tips though, it doesn't take much to make a big difference in someone's whose Weekly pay is $US150.) In general, it's cheaper on CC, snorkeling is $25 per person, and I bet you can bargain for the longer trips.