Another source of discount are the web cashback sites. I use quidco.
Is a bit complicated so you are best to read the stuff on their site.
For the basic RAC cover, the discount works out at:
Basic Roadside Cover £29 (as advertised at RAC.co.uk)
Quidco Cashback -£20*
Quidco annual membership £5**
You effectively pay £14
* Cashback takes a couple of months to be debited to your bank account
** Annual membership comes out of your cashback, you don't pay it up front
I use it for most internet purchases as a lot of the main retailers are signed up. For example, Interflora have discount and free delivery through the quidco site. Great for mothers day if you happen to be stood on a wind-swept bank.
