White berries spawn in an isolated area in Isafdar, north of the Tirannwn lodestone and just west of some adamant rocks. They respawn very quickly (about 4-5 seconds) after being picked up.

To get to the white berries area, use the lodestone in Tirannwn, and click the red dot to the north on the minimap (your character will need to walk northwest then east to get around the trees). Consult the map above if you're unsure how to get there. It should take about 15 seconds to get to the berries from the lodestone. It's possible you'll take damage from the tripwires on the way, but the damage is generally insignificant and you'll be fully healed by the bank.

Once there, just stand over the white berry spawn, clicking it whenever they spawn. After you've collected 28 of them, use the TokKul-Zo to bank, and repeat. Each trip takes about three minutes for a profit of 90,440. Once you've got enough berries, sell them on the Grand Exchange.

It's also possible to use a Beast of Burden to increase the berries per trip. Using a pack yak, you could collect up to 600 berries per hour, for an hourly profit of 2,261,000.

As all you need to do is click once every few seconds, you can do other activities like High Level Alchemy or Disassemble on noted items while you wait.