I'd give you the same advice I gave my folks - think about what you want in a "reader" (which is to say, do you just want to read books, or do you have a need/desire to do other things with is), then look at what each product and each model offers.
Personally, I can't imagine an entry-level version of a device being my choice when an extra $100 or so gets you a lot more functionality. But if it's really just a book-reading device you're after, the cheaper ones may make sense.
I wouldn't want to end up with a less-than-ideal device for your needs because it's what's affordable to you. You could always wait - either to build up some more funds or let the functionality get cheaper over time.
My folks were stuck between wanting a reader and needing more tablet-type functionality. Luckily the Kindle Fire was right in their sweet spot.
Also, I'd hitch my wagon to the Amazon ecosystem a lot more comfortably than I would to the B&N one.