Guild Wars 2 Spidy just came out with an epic addition to their site. Now they showcase the crafting costs and profit margins of selling crafted items. This is epic, but I'll tell you what can make it even more epic... using buy orders instead of buying crafting materials outright. If you use buy orders then you can reduce the cost of crafting items dramatically, which obviously raises you profit margin.
Good luck and let me know if you have any success crafting after using GW2Spidy.
If you need help with learning to use buy orders to make gold, try this free gold guide that I created.