PICK THE RUNS
How it is played
Faction
Region
Loot
Server
Two reasons. The pre-raid list, which is the dozen or so items that make a character worth bringing, and the rune quests, several of which are inside dungeons and cannot be done alone at the level you first want them. Buying runs a few at a time is how this is actually done, which is why the page is a catalogue with a quantity.
If the run you want is for a rune rather than for loot, say so on the order: the route through the instance is different and the group will stop where it needs to. It is also usually cheaper than the same rune bought on its own, because the group was going there anyway.