How about a used Motion Computing slate like this one on eBay?
http://cgi.ebay.com/Motion-M1400-tab...item4a9fa9599e
12" (30.7cm) screen, stylus touch screen, 1.1Ghz Centrino CPU, 40G HD, Win TabletPC OS, wifi, etc..
This is just one example. More available in different price ranges. My brother just bought one off eBay and it is in wonderful condition and works great. I think his winning bid was US$240 -- still cheaper than a large screen e-reader.
edit:
Here is a slate on the UK eBay site. Different model but still a 12.1" screen, 1.5Ghz CPU, 30G HD, on board wifi, etc.. £179 plus shipping.
http://cgi.ebay.co.uk/MOTION-COMPUTI...item53e0628d12