The Onyx Boox series come in different sizes and are just Android with a custom launcher, and they're cheaper and with more choice (most notably regarding screen size).

Caution however, the company violates the GPL, which might be a deal-breaker for some.

I got a Supernote and its a bit cheaper and has really great features. Remarkable shies away from anything but writing, so sync is limited - while the supernote has great calendar sync thats come in handle for note taking.