How to make a cheap custom android device?

Hi all,
I am interested in making my own cheap basic Android portable device for a hobby project.
What I need it to do is to have a data-only 4G connection (with SIM card) and allow me to use it only for surfing the WEB (Chrome), Gmail and messaging apps.
I need it to do well these tasks, but not more than this.
I thought about Android OS (because it's well secured), but maybe there are other possibilities that I don't know.

It shouldn't be stylish or pretty.

What I want it to have is:
- a responsive touch screen (5-7 inch)
- a battery for 12 hours of use (1 day is better)
- enough storage for the basic apps I stated
- enough RAM for the basic apps I stated

What I don't want in it is:
- NO Wifi
- NO Bluetooth
- NO GPS
- NO Camera

So where should I start from?
How cheap can it be? (my target is less than 100 USD)

I am an experienced board design engineer so I'm not afraid of PCB development, but I'm looking for the simplest and shortest path, and I don't have any experience with the mobile devices (phones, tablets) world, so I don't know what are the available chipsets for such projects.

Thanks!

Your first port of call is to Alphabet (aka Google) for a license but don't hold your breath waiting.

Brian.

Android is a operating system, similar to linux, windows and macs. I think (not very confident because I have not done it myself) you can install android on a linux or a windows machine- just download the required libraries and a few executables. You can run most of the apps (almost all the icons you see on the phone are basic apps) on the desktop or laptop running windows or linux (need to check for macs).

Then you need to owrry about the processor. If it can run linux or windows, then you should be safe. For example, arduino cannot run android but the raspberry pi can (again, I have not tried that myself).

Once you know that it can run on top of linux (or windows) you need to look for a suitable boot system. Then you can use the boot loader and use android directly. Considerable labour is involved but it should not be much difficult.

maybe you should get a phone with the appropriate size screen
and disable all the things you don't want, or simply do not use all the things you don't want
in the long run, it may be a little more expensive (or not) but it will work
you'll be able to use it as soon as you have the device

regarding the cost:
you can build Johnny Cash's Cadillac - see "one piece at a time"
"Well, It's a '49, '50, '51, '52, '53, '54, '55, '56 '57, '58' 59' automobile It's a '60, '61, '62, '63, '64, '65, '66, '67 '68, '69, '70 automobile.
LetsSingIt - The Internet Lyrics Database
"
you propose getting all the pieces and then putting it together yourself
that works fine for building yourself a computer, since once you figure out what you want,
(and there are lots of places to get all kinds of information), you can buy it all in one day
and it will be delivered in less than a week.

it may not work so well for what you want, unless you have the hardware and software expertise.

wwfeldman said:

maybe you should get a phone with the appropriate size screen
and disable all the things you don't want, or simply do not use all the things you don't want
in the long run, it may be a little more expensive (or not) but it will work
you'll be able to use it as soon as you have the device

regarding the cost:
you can build Johnny Cash's Cadillac - see "one piece at a time"
"Well, It's a '49, '50, '51, '52, '53, '54, '55, '56 '57, '58' 59' automobile It's a '60, '61, '62, '63, '64, '65, '66, '67 '68, '69, '70 automobile.

Johnny Cash - One Piece At A Time Lyrics | LetsSingIt Lyrics

Lyrics of ONE PIECE AT A TIME by Johnny Cash: Well I left Kentucky back in '49, An' went to Detroit workin' on a 'sembly line, The first year they had me ...

www.letssingit.com

LetsSingIt - The Internet Lyrics Database
"
you propose getting all the pieces and then putting it together yourself
that works fine for building yourself a computer, since once you figure out what you want,
(and there are lots of places to get all kinds of information), you can buy it all in one day
and it will be delivered in less than a week.

it may not work so well for what you want, unless you have the hardware and software expertise.

Click to expand...

I prefer to build it by myself, I want to learn from it

The reason I thought about Android is because it's already secured and gets security updates.
I suppose that Linux may be also OK for my purpose.

Any recommended hardware? raspberry pie is an option - will RP zero do the job or I need one of the more powerful versions?

Thanks!