If you need to travel at a moments notice (off peak) and need a walk up fare then London Midland fare from Crewe to London is £20 compared to £60.30 with Virgin trains. Surpsingly Virgin train and others (trainline/national rail) do not ellude to this fare.
OK it'll take you an extra 1.5 hours each way, but the fare is 33% the cost of Virgin's, which goes a way to compensate for the inconvenience. Virgin advance tickets are similar value, but remember these have to be booked a minimum of two weeks in advance to get similar fares. London Midland is a walk up fare which is much more convenient, and useful when you have that last minute trip.
Railcards also apply and reduce the fare to £13.20