[DNSB]

Personally, the last time I went through evaluating different ereaders was a decade ago. At that time, I looked at Amazon's Kindle, B&N Nook and Kobo's ereader. Currently, I own several Kobo ereaders and a Tolino epos (a Tolino is not a bad choice if you live in a German speaking country).

Since you are living outside the USA, you can drop Nooks from your choices and, going by the reports in the Nook forum, if you are living in the USA, a Nook is not a great choice. The current software is buggy and B&N does not seem interested in changing that.

From the devices I am most familiar with, the Paperwhite 4 or the Clara HD would fit into your price range. You can use calibre (and Apprentice Alf) to convert between formats so don't worry about being tied into an ecosystem. On a negative side, there have been complaints about the Paperwhite 4 displays not being sharp while the Clara HD has had complaints about a light bleed issue on the edges of the display (my Clara HD does not have the issue but enough photos showing that issue can be found on this site).

I'm not certain as to what the pricing on the larger format Kobos (6.8" H2O2, 7.8" KA1, 8.0" Forma) or the Kindle Oasis 2 (7.0") would be in your area of the world so can't say how they would fit your budget.

All 4 Kobo ereaders I've mentioned have ComfortLightPro allowing you to vary the colour of the frontlight.