Curious...

Assuming you have 5x 70's.

WotLK releases... Buy 5x WoTLK 4xBattlechest...
Recruit-A-Friend the 4 new accounts.
Transfer 4 toons to the new accounts.
Level to 80th 3x faster than anyone else.

Thats $120 for battlechests, $100 for transfers, any other cost I'm missing?

$15x4 refund (free time on main account) brings the total down by $60...

so $160 for 90 days of double XP and lots of free levels you can whore around. I'd bet you could fill 5 accounts with 70's in 90 days of triple XP.