It is hard to beat the Kindle WiFi for value. It has the latest Pearl EInk screen, with better contrast then the older Vizplex screens. You may want to add bolder fonts, but the originals and their size options are shown in
Can someone compare fonts for me?. These screenshots are actual bitmaps of the screen, but they are likely larger on your PC screen than on the actual device.
The Kindle does not "reflow" PDFs. It does have a landscape PDF viewing mode, but you may be better off converting PDFs consisting of text to MOBI using Calibre. Converting TXT to MOBI with Calibre is also a good idea for the K3.
You should buy a cover for any EInk device, which pushes the K3 over $150 with shipping. It is outstanding value for the money though.
There is no SD card slot, but it has 4 GB built in.