Ibanez (and probably other makers) has an entry level acoustic for about $100 USD at many music stores. I was pretty impressed with how well it played for the price and used it all during my last trip. When I left I gave it to a friend who was very happy with it. Another thing to consider - even if you could find a musician that wanted to rent you a guitar the condition of many instruments on the island not good. Some guitars never have strings changed and the bridge will be about ready to snap off the top because it just keeps getting tuned up (and up and up!). Few have decent strings, and I have seen many with deep grooves worn in the frets below the strings, bridge pins made out of scrap wood, etc. Needless to say they are not easy to play in this condition - I'm thinking you want to play well at your friend's wedding. Another option is to buy an inexpensive used guitar to bring. Good luck and have fun!