Actually you would probably make minimum wage which is usually around seven dollars. Plus half of it would go to taxes since if you had enough disposable income to spend on something like runescape gold your parents are probably in a high tax bracket.
This would then net you around slightly less than 1 mill a hour since most legitimate gold providers sell their gold for 4 dollars a mil. Add in middleman fees and additional labor to arrange the trade and it starts to look less and less attractive to purchase runescape gold.
In addition you run the risk of being banned and you gain no xp.