I would say 14m loss if you are alching.
I'm doing 80-99 right now stun alching. It's costing me around 25m.
Edit: Simple little formula to find out how much it will cost you if you are stun alching.
Subtract your current xp from 13,000,000
Divide that by 155(xp gained from 1 stun-alch)
Add the cost of 1 soul rune and however much money you lose from 1 alch.
Multiply that by the number you got from dividing 155 into the xp you need.
Should come out at a reasonable number.