Cost effective after cashback would make this deal £10 a month!
Looking around for new sim only deals I've come across Vodafone offering £120 quidco on their £20 sim only price plans. I have been with Vodafone previously and they paid my £100 no problem. Could be useful for some.
I wouldn't recommend this deal to any heavy usage internet users due to the 500mb limits imposed on data.
Quidco only offering this cashback amount until 3rd Jan 2011.