Sorry, guys currently I've been unable to find a f2p method, but I'll keep searching.

Method #1

1. Player A goes to taverly dungeon to pick up scales.

2. Player B buys an inventory of them for 19k each then drops the scales and keeps re-doing it.

My personal favorite method, works well.

Method #2

Requirements and items needed: ring of dueling, a rope, and 25 agility.

Steps:

1. With ring of dueling teleport to castle wars w/ both accounts.
2. Then head out and go west and you will find a small island that has
4 Jangerberries.
3. Now use your rope on the branch to get on the island w/ both acc;s.
4. get on island where the orges are they dont attack though.
5. each jangerberrie is 495 gp ea and they respawn fast.
6. collect them and sell to other account with money. Continue collecting while other accounts banks in castle wars.
7. Account giving will head back to area and then give money when another load is ready.

Method #3

Person A - transfering the money OFF this person
Person B - receiving the money

Both players will meet at kalphite soldier lair where 3 potato cactuses respawn.
They will wait at the safe spot for 15 minutes until the monsters are unagressive.
Then logout and in to make sure none of the monsters are following them.
Person B picks up a load of potato cactus and sells to person A.
Person A drops the cactuses and we begin the cycles again.

Method #4

Take the account with money & the account receiving money to the Whiteberries, that can be found in the wilderness
They spawn really fast!, The account receiving money Get's a full load of Whiteberries. Trade the whiteberries to the account giving money for GP, then the account with money drops them. Account receiving money Repeats

Enjoy guys, and if you have any to share, I'll be happy to add them on to the list.