Although it may be out of your budget and some here will not like it, but you might consider a windows tablet if its within your budet. Not the RT ones, but the Windows Pro tables. The Pro tablets have the full Windows 8 installed, and not the cut down version that RT has. You wouldn't be able to install Calibre or Sigl on the RT tables (that I know). The Pro tablets have USB slot and SD slot, and should be light enough for you. I have had the opportunity to play on one for a few hours and it was surprisingly nice to use, once I got used to the differences in the OS from windows 7.
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