Dekay: That there is proof that every market is totally different!
I charge wholesale price for my blank garments, plus 10% for waste/loss. We charge a per-order handling fee (same if they order 1 garment or 1000) which is nominal ($5). There's a printing fee per garment, and then there's a supplies fee (ink, pretreatment, Kraft paper, etc).
This way, people have little reason to bring in their own blank garments, since I am usually cheaper. In my area, there are so many places to buy "wholesale" blanks that I had to price things this way to stay competitive over the cotton shops.