I can tell you that I spend $50 at walmart and picke dup a canon mp495. I can scan receipts, pictures, etc, without any issues at 300 DPI, even better at 600.
As for what format you go with, it is really up to you and what you want to work with. My scanner's app brings them in automatically as jpg, I think, but really any format should work. (I prefer an image format over pdf, as pdf is more for a document, not an image).