Looked at the ebay offers and found this thing.

It's biggest advantages:

• 13'3 screen with quite low resolution (good to work with finger)
• really good life with keyboard attached
• i3 or i5 Haswell CPUs with hyperthreading .
• IPS screen, not the best in the world, but much better than on most slim notes
• upgradable
  • you can upgrade ram up to 8GB (it is just notebook DIMM)
  • you can upgrade SSD disk
  • plate to put 2.5" HDD or SSD inside keyboard part
• normal SD reader and HDMI on keyboard part
• can play high bitrate 4K without any issue

Disadvantages:

• CPU are special tablet modifications, so less powerful (slower clock)
• single channel RAM, but for the task it is not super important
• weight if you count both parts

Now it is $399 at http://www.ebay.com/itm/331249003429