12+ inches and cheap don't really go together.
But perhaps the
Sony DPT-RP1 might work for you, if you're willing to convert all your reading material into PDF format.
It also looks like it might make a good note taker.
On the cheap side, perhaps the Amazon 10" Fire tablet would be more what you're looking for? Although I can't see it at the Amazon.com store at the moment, only at the UK store.