I'm at 375 mining and herb, it's really just free money especially when your grinding in certain areas.
I have no idea if this is average, if it's above or below what other trades bring in, but in about 1-2 hours I can sell off 50g in vendor crap, at least 50g-100g in mining junk, and easily at amount in herbs alone, in outlands. If you find the right areas at higher levels, you can actually do both at once in the same area, hence why it's free money. You either make non-stop gold from kills, gathering, mining, or skinning if you prefer. And while your grinding, buy the best gear you can with gathering professions. The faster you kill, the more money you make in addition to gathering, and since your already grinding, I consider it free money.
But as mentioned, no idea how it rates to other trades. Other trades might make that total in one item created with the right recipe. I think 2 gathering professions are money in the bank without the headache of the huge overhead.
I do know that my alt is a few levels shy of outlands, and I'll be taking the 3rd gathering profession left for me to 375, and one actual trade itself up.
Edited, Mar 3rd 2007 9:34pm by Jarfas