Hmm, I remember sending a huge wad of magazines and it cost £32 but I was mis-sold that service.
I think recently I was told there is a 3rd Class 'Standard Parcels' service which can take a week to arrive but allows for items up to 30Kg.
I think it was either £15 or £20, but I could be wrong.
Getting a box and filling it with newspapers is going to be awkward though. I know a private courier will charge £50 but they'll collect it from your house and won't hurl it about a sorting office!
;-)