As far as cheap laptop style computers go I personally go for older run-of-the-mill laptops from a few years ago. Part of the reason is the screen is larger, and it's also going to be faster, and cheaper than things designed for this. The one I have now, for example, is a Dell 1501 AMD laptop for $200. I don't care about battery life at all though, I just have multiple cords. Though the one I have has one that lasts 3-4 hours, which is nuts for a laptop from 2007 (I think that's about when it's from anyway).
Though I will say, it being dual core is a step in the direction of becoming actually usable. Why does it have ubuntu instead of whatever windows that probably came with it?