Then you have to be able to sell it for enough profit so that its worth your time. This means, for the most part, no buying mats off the GTN.
Where you get the mats makes no difference to the price. The mats have the same value either way. If you can't sell something for more than the mats cost why are you making it to begin with? You'd be better off selling the mats instead of decreasing your net worth selling the finished product.