You will NOT be rich from a crafting profession just by learning what the trainers provide! You have to spend gold on schematics/formulas/plans/etc to make the stuff that people really want to buy. Im not saying that every plan on the AH is going to be a moneymaker, but the ones that ARE moneymakers youre going to have to pony up the cash. Dont bother farming for them its a waste of effort just pay a reasonable amount for it on the AH.
Guess what? Youve just put yourself above probably 75% of the other crafters out there! Why? Because 75% of WoW players either dont have the gold to buy plans, or they refuse to spend money on them because people price gouge on the AH. Now instead of competing with 1000 engineers, you are competing with 250 of themand out of that 250 there will be quite a few that arent as aggressive in making money like you, you sly dog!