I went with 5x DK's, and moved a Paladin onto the team.
Then switched to a Priest.
And ended up switching back to the Pally.

If you RAF, you level 1-80 in approximately 1/3rd the time.
If you do this twice, its 1/3rd plus 1/3rd, or around 2/3rds normal time... which is still a huge bonus.
Plus you get the granted levels.

You would need to purchase the accounts, which is the true cost.
When you pay for the first month of game time, the referring account receives a month free.
So that is essentially, free.
The second month (and the third) is useful if you still want to level toons (but you can boost a full account of teams, inside a month with a mediocre geared level 85 anything).
The second month is more a case of wanting the RAF Rocket or not.