Welcome to the forum! I'm no help on S. America, but I think for a lot of us, destination wedding ideas transcend their locals.
That being said, if you had a real adventurous bunch you could have a group hike Machu Picchu and get married on the trail. Probably not what you had in mind, but you mentioned Peru and that's what I think about when I think Peru In any case, happy planning and let us know how we can help!