Why is earth/water/air runes cheaper than OSRS Gold mind/(body) runes of the Grand Exchange ...Don't say "Supply and Demand" I already know that. While earth runes (39gp), water and air runes (22.2 gp) must be highly sought-after and consequently command more Grand Exchange prices, fire and mind runes (6gp), 5 gp and 7 gp are not as sought after due to their Grand Exchange prices being comparatively low.
Air runes are relatively inexpensive because (1) runecrafters have the ability to make the most air runes than any other rune (increasing supply of air runes), (2) air running has a lot of popularity (again increasing availability) and (3) people would prefer to buy an air staff instead of a fire/water/earth team (decreasing market for air runes). However, air runes are priced at 22 gp and cost more that mind/fire/water.
Why are earth runes (39gp) and water (37gp) more affordable than mind/fire runes? Just curious. Some reasons; Water runes are often used to aid in blitz or barrage which is very popular in P2P. These are very rare drops of monsters, and are not a typical craft.
Many monsters drop large amounts of Buy RS 2007 Gold fire runes. Mind runes are relatively useless. Keep in mind that air runes are those that pop up in standard-spellbook spells the most often. Because they are almost ineffective and are extremely affordable. Earth runes are employed in the Vengeance spell, which is 10 at a time, and the spell ends with p2p and pking.