I think the dollar store bags are cute and great for a destination wedding, I would use them because people will probably be getting them wet and putting messy things like sandy towels inside them and they may not want to ruin the nicer bags. Then you can use the extra money to put some more things in the bag maybe hats, t-shirts, or towels? It depends how many bags you are making but those could be a nicer item to put in them.