I want to Karazhan last night with my priest. Great short run, killing everything from Attumen to the Curator. I now got over 100 badges of justice, which might come in handy when patch 2.4 hits and I can buy great loot with them. Anyway, we also did the opera, and by some statistical fluke whenever I'm in the opera they show Romulo and Julianne. Only saw the Wizard of Oz once, and never have seen the Big Bad Wolf. So Romulo had as loot the Trial-Fire Trousers. Not really a healer item, but due to the 3 gem slots it ends up being better than the Hallowed Trousers I was wearing, so I applied for and got that loot. So far so good.
Now I had Silver Spellthread on my old trousers. But as the new trousers are epic, and will probably have to last me for a while, I should put the best possible enchantment on them: Golden Spellthread. Now that went for insane 450 gold on the Horde AH, so I bought it for a far more reasonable 230 gold on the Alliance AH and had my wife with her account help me to transfer it. Then I need to fill the three gem slots, preferably with Teardrop Living Ruby for maximum healing. 70 gold each.
So in the end upgrading my trousers will have cost me 440 gold. If I don't do much else, I can grind 100 gold a day, but given my other activities it's closer to a week of gold grinding. And that's just the pants, I paid also around 500 gold for the healing enchantment on my epic mace. And there are a couple of items I'm wearing which simply aren't enchanted yet because I can't afford it. If you gem and enchant a full set of epics with the best possible enchantments, which is kind of expected from you if you raid, you can easily spend thousands of gold! That is far, far more than potions, other consumables, and repair cost will set you back.
It is mainly the cost of gems and enchantments that make raiding so bloody expensive.