How much do you make from 99 Runecrafting?

Well, first I don't know if you're talking about money, or runes, so I'll explain both. At level 99 Runescrfting, you can make 10 air runes per rune essence. Just below that, you can make 8 mind runes per rune essence.

Now, money. Each air rune is worth around 9 to 13 gp. So if you get a full inventory or rune essence (28) you will get 280 air runes. Times that by the average price or air runes (11gp), you will get around 3080 gp. Not much. You're better off making 2 natures per rune essence. You can do that at level 95 Runecrafting.