Making free Runescape money collecting flax can be very profitable. Although it is the cheapest item you can collect from this Rs guide, it is the closest to the bank. Being close to a bank means more trips per hour! Another great thing about collecting flax is the amount of flax in the patch you can collect from, which is located south of Seers Village.
To get to the patch, you have to be a member. (If you want to get to the part of this Rs guide which gives insight to a free to play item, go to the next section about red spiders' eggs.) You can start by going to Varrock and getting a Camelot Teleport tab from the Grand Exchange or use your magic with five air runes and a law rune to get yourself outside of Camelot, which is right next to Seers Village.
Head west after you get to Camelot and you will run into the Seers Village bank. If you head directly south from there, you will hit the large patch of flax where you can collect all you want to build up money in Runescape 2. They respawn fairly quick and it isn't too populated, so your trips will go fast!
Each one you collect is currently worth around 82 gb and each trip (collecting 28) will get you around 2300 gb.