I've just started Muay Thai within the last month. My experience, the school let me take a free lesson (how the hell are you supposed to know if it's for you or not?) and I enjoyed it so much that I signed up right after class. It cost me $390, which included a $99 one time sign up fee, the first month and mouth guard, hand wraps, King boxing gloves, t shirt and combo manual.
The first lesson, be prepared to WORK. I play hockey in a rec league and I've been so short benched that I was forced to play for 40 minutes without subbing...and even that was nothing compared to the workout you'll get from Muay Thai. Expect to feel like a tool for awhile until you start to get used to the movements a little bit, expect to sweat and be dogged tired. I go 2 times a week for roughly an hour, but once I start to feel more comfortable with technique and stuff, I might go more often (I can go pretty much every day of the week and there'll be a lesson).
Y'know what, I wouldn't join the school you just mentioned, what's with the secrecy? Find a school with a trial class and give it a shot, I know I love it...and I'm usually a lazy bastard.