Today only, the Kindle DX is on sale for $299. I have really enjoyed mine. The larger screen size helps when reading PDF files. This is important because many old texts (like from the 1800s, 1700s, 1600s) have not been copied over into computer readable text. They are images only. Reading a PDF allows you to read it the way it was originally printed. Some of the OCR (optical character recognition) versions have a lot of "trash" characters that distracts from the reading experience.
I've been reading both Dabney and Manton in PDF version on my Kindle DX. Here's the link: