Did some calculations on how much cloth you'll need to turn IF you have a level 80 toon who will access to all four Donation quests, the repeatable Runecloth part, and if you really don't want to bother doing any Worgen/Goblin quests to help with your faction rep grind:

From Friendly to Exalted:

Now unless something changes, at Friendly you start at 100/6000 or 5900 points away from Honored.
By turning in the first four Donation of... quests which give 350 rep for each you'll then be 1500/6000 or 4500 points away from Honored. And with the first four Donation of... quests done the repeateable Donation of Runecloth becomes available.
So with that now available to go from Friendly to Honored you need 60 stacks of Runecloth.
(1 stack/75 rep x ?(unknown stack)/4500 rep. Then cross muliply and divide to get 60)

From Honored to Revered 160 additional runecloth stacks are needed.
( 1/75 x ?/12000. Then cross multiply and divide to get 160.)

While from Revered to Exalted 280 additional stacks are needed.
( 1/75 x ?/21000. Then cross multiply and divide to get 280 )

So when adding together the 60, 160, and 280 additional stacks you'll need a total of 500 stacks to turn in for the repeateable Donation of Runecloth quest. But also remember you'll need 60 stacks of Wool, Silk, Mageweave and another stack Runecloth for the Donation of....quests.

If you don't have anything better to do while waiting for a Beta Invite and you're actually serious about getting your level 80 toon the Worgen or Goblin mount then for the best runecloth drops just go and farm Stratholme. (Not the Caverns of Time version but the regular one.)
Or just farm it now so you can give the stacks to whichever Alt you plan to grind Worgen/Goblin rep with so you want have to waste money in the AH later on.