If you can endure long delays for the phone call, I find PN staff very willing to talk discount. I have an excellent package with unltd calls/FTTC including line rental in advance for about £28 pm on a two year contract. I don't mind this long contract as reliability and performance have been excellent.
My only problem has been with every change/renewal particularly this year when PN launched its new account system. They get it right eventually and hopefully it will perform properly in future.