The $300 10.1" ASUS 1015E-DS01 Notebook is probably your best bet. That's the smallest size screen you are going to find as far as I am aware of. The screen resolution is only 1366x768 so the PPI is going to be lower than on a mini-iPad. http://www.newegg.com/Product/Product.aspx?Item=N82E16834230936
If you want higher resolution on a small screen then you need to step up to an Apple MacBook Air with a 13.3" 1440x900 resolution screen. There are also a handful of laptops with a 13.3" 1920x1080 resolution screen, but they cost more than an MBA.