I was on the same boat about 2 years ago. I decided to get a cheap windows 8.1 at the time, it was almost 10 inches which is good for reading but on the other side a little bit heavier than the more common 8" ones.
until today it runs windows 10 with no problems. I prefer windows because of the flexibility. also should I have chosen an android tab, it would likely be still stuck in say kitkat OS instead of the latest one today.
while specifications should be considered, the most important asset of a reading tablet is the display. my tablet cost almost 200$ in late 2014, it is by no means a superior tablet, but it has a respectable viewing angle from all 4 sides (which is very important for a reading tablet) and a 1366x768 screen resolution. for the same amount of money you will get a better tablet today. but im not sure how good a 50$ tablet would be for reading because the resolution seems to be at only 1024x600.
it's probably best if you could look for the tablets in retail stores instead of webstore, because only then you can judge the display quality of the tablet (resolution, color, viewing angle, etc). the newer ipad would likely be a winner in terms of display but it comes with a heftier pricetag.