Someone on Trip Advisor recommended Sean at Holidaze. She said she's used him for many trips. Holidaze is out of New Jersey and they do a lot of groups, too. Website = holidaze.com
1 800 526-2827. Ext. 15 for Sean.
I'm using him for my August trip to Termas de Chillan and he seems to know his stuff. They do all the S.A. resorts and get a bulk rate on LAN flights so you save a little bit of money.
P.S. If you do decide to book your own flight via American Airlines or LAN, (they code share), here's what I discovered: AA flights are a LOT cheaper if you book them as code shares on LAN'S website, NOT on AA's website. They're even cheaper than LAN. It's so bizarre, but true. (Well, at least it was true 6 weeks ago.)