I really, really, really don't understand why everyone is screaming that healing costs so much mana.

I run protadin, disc priest, ele sham, destro lock, arcane mage And the only character that runs oom is my mage at times, because of chainspamming arcane blast.

It has to be said that the protadin has quite good gear now about 10 rare 308 pieces. But even when queueing with just my priest I hardly run oom. You just have to completely change the way you're healing. For a disc priest, only ever cast flash heal if there's no other option and greater heal might land to late. I even spam smite when i can for the 5 stacks = +15% healing and mana regain.

You have to check what spells costs and what they heal. The standard spammable spells have their costs increased indeed, but aslong as you can avoid those by casting every other spell when you can I don't really see a problem.

(my priest gear was mostly lvl 70 epics still, in full cata uncommons now(thanks to Auction house)

I'm with you on not managing other instances though. The new dungeons require A LOT more movement which is quite hard to manage. Beside that i personally still need to learn to heal. I spam smite 70% of the time which heals through Atonement. Messing around with Repeater Regions since yesterday.