E-readers have become a commodity. People are practically throwing them away, holding to their somnambulist part of the feature upgrade treadmill.
As others have pointed out, you are buying into a whole system of DRM, file format compatibility, legality, and so on. You have a learning curve ahead of you.
My advise is to get the cheapest one you can get you hands on. See if someone you know is going to toss away an older model. You might be able to get one for free. I did.
With that, you can get a feel for what they can do, and what features you might want that are missing. If you are happy as a passive consumer you will then be well armed with information before you pony up for an expensive model.
Hopefully what you will soon see is that there are whole other systems out there that grant you some serious freedom. DRM stripping, device jailbreaking, vast online libraries of free content, the range of different file format superiority, file format conversion, and more.
You'll discover Calibre.
My little obsolete well known name brand device has an intentionally disabled wireless, the advertisement nagging cruft is long gone, various crippleware features tossed, it's perfect for me. It didn't cost me a penny and I'll be using this until the battery or solid state drive dies.
E-readers don't replace books, but they're great for the niche they fulfill, and the inadvertent user supported systems and freedom infrastructure they've given rise to.