Maybe I'm a pretty standard size, but is there really a huge demand for custom-fitted t-shirts/henleys? Custom fit is valuable for clothing that is three-dimensional (suits/sports coats) and/or has many different fit parameters (dress shirts). For the segment of people that are interested in custom-fitted clothing, is a custom tee significantly better than an off the rack one? I guess I'll answer the question for myself - buying the $99 package.
On a side note, some feedback on your checkout process:
As a guest, when I go to check out, after I register/log in, it takes me to a referral page instead of the payments page. That was really confusing. You should be taking people straight to the payments page if you want to maximize your conversions.