I think I must be the only person who has never hired a sim before my airline interview. All I did to prepare was practice on an AGK Mk 6 at work and microsoft flight sim. You really don't need to spend all the money, get your scan up to speed and trust yourself. The airlines don't expect perfection, they expect you to be able to fly and improve through the session. My attitude going into the 747 sim was to enjoy it as it maybe the only time I ever get to fly one.