Is the price for a Sony PRS T2 or Onyx Boox i62 your top limit? The point of my question is that you most probably won't become happy with a 6" reader if you want to read academic papers or pdf files on it. For this you will need a 9,7" reader like Onyx M92 or Pocketbook 912. Or a tablet, like many members here will advice. But the bigger readers will cost a lot more.
Also, converting epub to pdf might prove difficult. Most probably you will lose the layout and you will have to do quite a lot of manual work after the conversion.