The best way to become rich, is start of by skilling.
you can do anything, start of by thieving, so it makes you a little cash, then try crafting you can make roughly 8m from 11-99 crafting
Smithing is really good for money making, get 85 smith and you will be able to smith rune ores and make a lot of money.
Once you have quite a bit of cash, you could start getting your combat up, as you would have enough cash to buy any amour or weapon you like.