I mentioned this briefly in my mining post, but Titansteel Bars are one of those products that seems to be used for just about everything. Check out the Wowhead "Reagent for" tab, and you'll see what I mean. It is also used in very large quantities by the more popular items, like the iLvl 264 BoE crafted items. One way or another, titansteel is one of those things that seems to have bottomless demand and is therefore an excellent product to sell.
High demand means high profit?
OK, so it's not perfect. Titansteel may always sell quickly, but that just means you'll have more competition. Also, every buyer has a fairly good idea of what market price is, so when the supply dries up, you can't make too much of a premium. Let's look at your costs.