I'm not sure, but I see what you mean.
Money wise it's not a problem. It costs £35 for the Battle Chest, Cata and MoP - which seems reasonable. It's also worth noting that new players are not obliged to buy Cata or MoP so they do not have to spend lots of money to begin with. WoW also goes on sale relatively often which is worth bearing in mind.
So no I don't see pricing being a problem at all. A person can spend £10 and get 1-80 content and a months subscription and thus aren't pigeon holed into dishing out large amounts of money to try out the game. Additionally if I'm not mistaken they removed all playable races limitations with MoP, so a new player has the option to play Worgen, Goblin or Pandaren as well. Also WoW has a very easy to understand trial version.
The other thing that came to my mind was the idea that levelling from 1-90 would be a challenge. However experience need to get from one bracket to another is always reduce by a significant margin with each new expansion. Then there's recruit a friend to help them as well.