Difficulty: Hard
Money Needed: About 300,000-350,000gp.

This is a common way to make even larger profits of money from merchanting and it is called Big bone merchanting.

To start (make sure you have around 300k), simply go to Varrock west bank and start buying as many Big Bones as you can for 300 each.

Don't bother trying to buy over 1k or more Big Bones in a not-so-populated world, because most people will transfer to world 1 and sell there instead.

Once you have around 1k (or more) Big Bones, go to world 1, same bank, same place and sell all of them for 400 each!

There you go, although it can take a long time to buy all those Big Bones, the huge profits you can make should keep you quiet!