The only confusion peeps ever seem to have, is how the purchasing system seems to work.
The Bird in Ashran.
3 can be bought a week. However if you have a lv 3 Warmill/Bunker it will give you 1 (of 3) for free. You can use Gold, Garrison, Crystals, or Honor to purchase the rocks. Each time you buy one, to use the same resource again, it will cost more (resets each week).