If I was in your situation I would probably buy a second-hand Sony Reader.
I have a gut feeling that in the near future there will be quite a lot of Sony Readers for sale.
With the PRS505 or PRS500 you get the best value for your money IMHO. Especially if you are not afraid to convert your reading material.
Whatever reader you buy you will still need to convert files.
Forget PDF files, espacially if you have bad eyesight.
The best thing you can do with pdf is to extract text and convert it into whatever format your reader will accept.
PDF is optimized for preserving printing layout, so even with the most keen eyesight the vast majority of pdf documents out there are barely legible on a screen that has 120x90mm
Go ahead and print out A4 pdf file on papers that have 90x120mm (that is the size of an e-ink screen (unless you want to invest in Illiad)). Use dot matrix printer. Now try to read the result. Bad, ain't it?