I use a Kobo Clara HD. I think Claras are the second cheapest ones. No colour. I find the contrast about as good as a cheap paperback book. Not as good as good quality printing on acid-free paper, but that's OK.

I actually prefer lower contrast, it gives me less eye fatigue and I've specifically chosen low-contrast themes on my computer for as long as I can remember.

I think there is a way to not create the account if you really don't want to. I put KOReader on mine straight away and never use the built-in software. That also incidentally has an option to adjust the contrast.