If you're exalted with Argent Dawn it costs you nothing to get into Naxx.  I've been wanting to work on hitting exalted with them for this reason, and because it's a long standing goal.

per http://www.wowwiki.com/Naxxramas :

[url=http://www.thotbott.com/q9121]Honored[/url]:  5 [item]Arcane Crystal[/item], 2 [item]Nexus Crystal[/item], 1 [item]Righteous Orb[/item] and 60g
[url=http://www.thotbott.com/q9122]Revered[/url]:  2 [item]Arcane Crystal[/item], 1 [item]Nexus Crystal[/item] and 30g.
[url=http://www.thotbott.com/q9123]Exalted[/url]:  Free

I'm assuming you need at least honored rep with Argent Dawn to be able to run Naxx.  The quest for attunement is [60] The Dread Citadel - Naxxramas, given by Archmage Angela Dosantos inside Light's Hope Chapel in Eastern Plaguelands.  After you're attuned there's apparently a &quot;Teleporting Spire&quot; (an open ziggurat) in the middle of Plaguewood (39,26) in Eastern Plaguelands you enter to be teleported to Naxx.

I've been hoping to get my priest up to 70 so I can just run Scholo a million times, &quot;alt+tabbing&quot; him with Kray to get Kray from revered to exalted.  I never figured on running Naxx, but afaik it's the last attunement Kray needs for full attunement of all pre expansion dungeons.