When I was there last year, T-Mobile prepaid had ridiculously cheap broadband. I want to say a pound a day, 2.50 a week, 5 pounds a month. This works best with a smartphone that can tether your laptop, but any phone that could browse the web could benefit. They also have USB dongles that plug directly into a computer and give wireless internet, though I don't know what the finances of that are, I know of it only because my first host had one.

("Free internet!" Yes, via a single piece of hardware that we have to alternate using...)