Yep the level 40 mount coasts what your other lvl 40 spells cost to train.
You don't say if you're alliance or horde. For the alliance epic quest, here are a couple of guides:
One and
the other Here's a
horde guide.
If you're a belf it's going to be significantly easier. The holy water for alliance pretty much just sucked. It's BoP so you have to get it yourself. You can't get a PUG, if you DO get a PUG then they're all tools, and half of the time they'll raid all the chests and then leave group when they get their water (we're talking non-paladins here just getting them for some random EPL quest) they bail.
That said though, it was a blast and I'm glad I did it. After several crappy PuGs to get (and failing to get enough) holy waters, my guildies took pity and I think we knocked out the waters one night and then the DM and Scholo bits in about 2 hours. It took us longer to GET to DM than it did to do the quest piece :-)