IMO,
MoP-
RoP id say 5k -10k is an average price more valuable on horde side due to no ellos band quest on horde side . As for Petros 1k - 2k max unless depends if you know how to glitch armor kits on them if you don't, they are useless if you can your looking at the best agility glass canon pants a 24 sub rogue can use.
WOD -
Rop precision may soar all depends if agility wearers are trying to go with a crit set , such as rogue with ass spec only ( crit build) or hunters (crit build). Petros depends how it scales in 20-29 bracket may make a comeback if Blizzard unsoulbound armor kits or knows glitch.