Make money with cooking.

Cooking level 1.
Purchase raw anchovies on grand exchange.  Then cook.  Resell back to grand exchange for profit.  Makes about 50k an hour.

Cooking level 35.
Purchase pizza base, tomato, and cheese from grand exchange in a 1:1:1 ratio.  Combine them to make uncooked pizza.  Makes nearly 1 mill an hour if you have a ton of starting cash.  The more cash you have when you start the more money you make because the cheese, tomato, and pizza base take so long to get on grand exchange.

Cooking level 45.
Purchase flour, tomato, jug of water, cheese, and anchovies off grand exchange at a 1:1:1:1:1 ratio.  Make them into pizza base by combining the flour tomato jug of water and cheese.  Cook into regular pizza.  Then add the anchovies.  To make anchovie pizza.

Cooking level 55.
Buy plain pizza and anchovies.  Combine them to make anchovy pizza.  Resell for profit.