[dodgyb]

I came across this beauty a couple of days ago> Not seen it in the flesh but is does seem to fit your use case.

https://remarkable.com/

Specs

https://support.remarkable.com/hc/en-us/articles/11500455428...

I use a refurbished 1st gen sony xperia 10.1 tablet that I bought for £100 on ebay. It is very light and has good resolution but the screen could be a bit bigger. The big plus is it takes an sd card and also a portable s/hdd can be attached so storage is no problem.

[konradb]

I have one of these; I got it specifically to read large PDFs on. I like it very much. The software has been a bit of a journey but broadly works. As a bonus you can ssh into it and screw around if you have the time or the inclination; there is a bunch of people who experiment with it. I just stick with the reading. It isn't backlit. But it is a beauty, having such a large e-ink screen is fantastic and being able to take notes/draw diagrams etc is great.

[ApolloRising]

600 is a lot