When it comes to ebooks, the IQ lets you have the best of both worlds; both Kindle and ePub. You can buy from Amazon or get library ebooks on it. Pdfs? Well, check here:
http://www.the-digital-reader.com/20...id/#more-14050
Understand that pdfs don't do particularly well on *any* ereader at 6in or under.
If you deprecate that requirement you might do well with the Kindle 3 WiFi (if you can find one), Nook, or PB360 which are all priced under $150. If you can find a Sony that low it might fit.
You do need to decide upfront where you're going to get your drm'ed books from, Amazon, B&N, or the other guys. DRM-free content can be used on any reader either directly or through quick-n-easy conversion.
If PDF display is non negotiable, you might want to go a bit higher (to $199) and look at the Pandigital 9in Android tablet:
http://www.the-digital-reader.com/20...ndroid-tablet/