It is all a matter of how you choose and how high your levels are in order to make money.
- If you woodcutting is 60, you can chop Yews. Those sell for a hefty price. You can make some money off of those.
- If you can do Telekinetic Grab, you can go up to the Chaos temple and preform that spell on the wine. The wine sells for a lot. But you need the Runes in order to preform the spell. Don't steel it by hand, the monks there will kill you quickly.
- If you cooking level is high enough you can sell the high class foods you can cook.
- If you can mine clay. Mining clay sells fast in the G.E. and sells for a good amount of gp. If you continue to mine it, you will make a good amount of money.
The higher the levels the more you can use your abilities to make money.