If you just want to get your chars to 80 then why not take Blizzard up on the option of a 10-day trial of Lich King?

On my 'vanilla+BC' accounts, in battle.net, I have an Upgrade option of "Free 10 Days Trial" of LK...


If you're only going to level them to 80 and then transfer, 10 days should give you enough time to rip through LK