It's a common misconception that it doesn't "cost" you to skill up a crafting profession, if you gather all the mats yourself. This is wrong... and I'll explain why.

First, consider your base income rate. Meaning, if you spend 1 hour optimally earning gold, how much do you gain on average? At L70, a fair average would seem to be around 100g an hour, depending exactly on your class and server economy.


So given that: what about the cost of leveling a profession if you buy the mats or gather them yourself? Simple. Buying will normally always costs you less than farming. Simply put, if you can farm more mats per hour than you can instead earn gold and then buy off the AH... you've calculated your income rate wrong! If you can farm X amount of material in 1 hour, and you can buy that same X amount of material for less than your income rate, you are costing yourself the difference. You should really only farm for things if it is your optimal gold-earning activity. Or, if what you want is simply unavailable on the AH or not in the quantity you need (and even then you should consider buying over time if feasible).

Also, consider the time you spend skilling up a profession. To go from 0-375 even if you have all mats on hand and simply need to press the create button 375 times, this will still take a good while. An hour or 2 at least. Unless the product of your craft as you are leveling nets you an income of at least your base income rate , this time spent leveling is a loss. Furthermore, it does not matter if you spend this time as you are leveling up, or spend it after you are L70, the cost is still the same. This isn't a huge cost, but almost everyone seems to overlook it.