Ele wand 6 is cheaper because it's more common (from mush shrine gach). It's also for the poison element amplification which f/p and I/l don't need therefore bishops which just need TMA like to use it. Technically bishops can use any wand so they go for the cheapest/highest TMA wand. Ele wand 7 amplifies ice which every I/l needs for blizzard.
Also luk isn't thaaaat bad. Let's Let wear stuff like doros->Calas or anakmoons and eventually stuff like lapiz sandals so it all adds up from secondary luk on gear