so in the example in the link you posted: the cost to consumer for the shirt-(white on black tee) is $11.85. my profit is the difference between my selling price and the cost of $11.85? (and i'm only asking because the FAQ on the site is REALLY thin on tangible information)
The cost that a merchant pays for a t-shirt is going go vary on the number of colors in the design, the t-shirt style they select, the number of shirts they order for inventory, etc.
i'm hesitant to "join" yet. i'm in "shopping around" mode now, and looking for a long tern vendor for fulfilment.
There's not much to "joining". It's free to join. You don't have pay anything to signup and look at the pricing (which will give you a much better idea of what your particular job would cost). If you don't like it, you aren't locked into anything (there are no monthly fees). If you decide you don't want to use it, your account is automatically deleted after a long period of inactivity (or by request).
any insight from an insider as to why to choose mojo?
Well, I don't want to get into too much self promotion for PrintMojo here

, but you are welcome to contact me off board or use the contact info on the site.
I'll be the first to say though that the service isn't for everyone. Some people prefer the print on demand method with no upfront costs. For those that prefer screen printed/embroidered garments and don't mind carrying inventory to make that happen, then it could be worth looking into PrintMojo.
It depends on your business model and needs.