The exile runes can be made during and after the Supermassive Black Hole! quest. After the quest, it these can be sold to the Monk (at the Portal to the Void Elemental) for the total median price of the runes. It is advised not to high alch these runes, as the total price of the runes needed to make one is much higher then the money you get from alching it. The only use for exile runes besides the quest are some spells in the Arcane Spellbook, although they are rarely used, to to their high value.