Get it and sell it.
So…you want to know what to get and where to sell it, eh? No problem. Here is some ways on how to get it, and sell it.
Here is the tip that my friend taught me.
You must have completed the Rune Mysteries quest and be a member to runescape to follow this tip.
First, go mine 27 rune essence. Then, go to world 66 (members) and go to Entara. This is the island that you cannot bring weapons or armor because its Saradomin’s will. Do not make the essence noted. When you get there, go through the church and head left where a bunch of people are standing. Trade with the people in the Zamorac robes (the red robes. However, there is a difference between the red and the Zammy. Trade with anyone in red). If they decide to trade with you, put up 27 rune essence. They will put up 27 law runes (because this is the location of the law temple) and 27 noted rune essence. Accept the trade. Keep building up the laws and then sell them for a bunch of money since people are really going nuts for them. Or, you could keep them for yourself, of course, but you wouldn’t get any value out of it.
IMPORTANT MARKET UPDATE!!!
The law rune market has changed! Now law rune makers will only give you a fraction of law runes for 27 rune essence. However, they will say it though. Example: "Open. 15/27." Some of them will give you all 27 but will not give any essence back. That's why some of them say 'No bak (back)."