I'm planning on doing both, having my florist provide a simple centerpiece, but then decorating the tables with additional vases (probably various sizes of hurricane glasses with sand, seashells, candles, etc) myself to cut costs. Besides the Costco, there is a Walmart in a strip mall along the main highway between Cabo and San Jose, which might be helpful for decor. There is also a large Mexican blown glass warehouse called Artesano's under the main highway leading into downtown Cabo. It will definitely have what you need, but you might need to be willing to bargain for the prices.
