The current price of a Vex Rune is 6 - 8 fg (d2jsp forum gold) and the equivalent in rune value is 2x Ist - 3x Ist.
Rune Information
Vex RuneCan be Inserted into Socketed ItemsWeapons: 7% Mana stolen per hitArmors: +5% to Maximum Fire ResistHelms: +5% to Maximum Fire ResistShield: +5% to Maximum Fire ResistRequired Level: 55