for a small screen, even 50-60 for a china special tablet these days. to accomplish your one button loads a website request, you'll need to open the website the old fashioned way once in CHROME, then go into the "..." menu and choose "Add to Home Screen". This will create a shortcut direct to the website.
Of course, the seniors will find ways to turn off WiFi, or otherwise corrupt the tablet, mine 95 year old grandmother always gets nervous when she "breaks" the tablet. despite asking not to touch any other buttons, they always do. Airplane mode is a favorite to turn on and then "nothing" works.
10-13 inch tablets are harder to find cheap, that's the only part of the device that costs money to manufacture. 13 inch chrome book are cheap, but not the touch screen ones
2013 KZ Sportsmen Classic 200, 20 ft TT
2020 RAM 1500, 5.7 4x4, 8 speed