I found a cheap deal with a code on a Family Railcard! It is half price till the 31st of October, that's £10 for a year instead of £20!!! Here is the information about it, and hurry it ends in a couple of days.

Using a freely available code it’s possible to buy the Family Railcard for £10, half the normal price of £20 (this is currently a trial offer as National Rail Enquiries tests whether it’ll work). Simply go to the Family Railcard website, complete the application form and in the promotional code box enter either of these two codes:
FRACXG10 or FREXPN10. Offer ends 31 October. http://www.family-railcard.co.uk/

   This is a great way to get out and about on homeschool outing cheaply and it makes the journey there part of the outing instead of something to be endured on the way. Hope someone finds this useful!