The least expensive ereader, out of the big brands, I guess would be the Kobo reader. Sony is more expensive. eReaders with LCD screens can be found as good deals right now at Best Buy & Future shop, such as the Aluratek Libre, but that's a whole different kettle of fish. If price is your primary constraint, I'd probably suggest getting the Kobo on one of it's sales, which would drop the price a bit, Chapters puts them on sale occasionally.
The Sony is more expensive, and I understand that it's dictionary support is pretty good. I can't speak for the dictionary on the kobo, and the only sony I tried is the older model, the PRS-600, as I don't have the new one yet. With the Sony, you can put books on from wherever you please, including the library.
Sorry wish I could be more help.
Last edited by Gadget_girl; 11-29-2010 at 06:09 PM.