I bought my nova pro on ebay for 200 euro incl shipping etc. That price is good but not especially unusual. You have to be patient. They come up at good prices, normally several at once. The nova pro 1 and note 1 will be cheaper now because the new version is out. Try looking on a international ebay search.
https://globalesearch.com/#!
Try onyx boox and likebook. I am not sure a 7.8 would work for you. 10" would be better, even in landscape. I think the Onyx software handles pdf file better than a likebook, but they cost more.