Linux

Pinetab 2? https://pine64.com/product-category/pinetab/

check out dell latitude 5285/5290 2-in-1. they are Surface Pro lookalikes with detachable keyboards, but with way service-friendlier interior - easy to open and SSD, comms, battery can be easily replaced, whereas RAM is soldered. the screens (12" 1920x1200 IPS mutlitouch) are gorgeous and the hardware isn't too shabby, kabylake (7xxxu) and kabylake-r (8xxxu), with standard UEFI BIOS so you can install Linux and have SecureBoot even. I can get them locally for $100-150, dependent on config and equipment (even less if they're without battery and keyboard).

edit: yeah, I misunderstood your idea, I thought you wanted a cheap linux tablet. what you actually want is a fantasy - an ultra-portable device with huge battery autonomy running linux and such a thing doesn't exist, for any kind of money.

namely, the mentioned dells are twice the heft of a normal android tablet and the battery autonomy is laughable; not only is it not an improvement over a normal laptop, it's likely to be worse, as that thing's essentially a laptop with extras, like touch, gyros, etc.

then comes the real hammer - touching the thing. Gnome and Plasma (and their derivatives) have touch support but if you're coming from an android or iOS tablet, that support is in its infancy. it's crude, inconsistent, flaky, and not very well propagated throughout the system. it's way better than it was a few years ago, but this is not something you'll want to hang your career or education on.

you can tweak the thing into something semi-usable, and for the price (around $100) that's a worthwhile endeavour and cute hobby project. it bears repeating, it is not daily driver material, and that includes way pricier solutions - saw a Ryzen 6-series the other day for like $700; everything I've written applies to it as well.

Have you looked at ubuntu touch supported devices?

That might do some tablets - although i guess they're focussed on phones - and I think have very little resources.

I was in a similar boat, and ended up buying a used convertible tablet from eBay instead. Much more Linux friendly, 12” Toshiba Dynabook. Might be a better option.

For proper desktop Linux in that price range a used surface is a choice. It'll be bigger and less battery life than an android tablet and I don't know what the fan situation is in the generations in that price range now.

Another option is go with an Android tablet that has LineageOS support. You get fullish access to the system, but the system is still Android, so depends on what you want if that works for you.

A second hand old Surface Pro could work well.

You are making a mistake. You are comparing an Android or iOS tablet, that have a user interface that makes sense for these devices, and you're trying to shoehorn Linux in them, and expect the same "fine enough". It won't be, because while it might work, it won't be ideal. Linux was optimized to be used as a desktop OS, with a mouse or touchpad. You'd have to install something like LineageOS to get it working properly, but then you will lose the cool abilities of a linux desktop for the most part. Conclusion: get a tablet if you want, but don't throw away your laptop.

Edit: Also, this was posted just an hour ago https://www.youtube.com/watch?v=H669Fwtv-3o

I miss Netbooks. Chromebooks suck, but most can be formatted and have linux installed

The Lenovo IdeaPad Duet works with postmarketos (mobile Linux), keep in mind considering your price range and considering its a tablet you're lucky to get 4gb of ram at most.

I think any Linux device with out a proper keyboard is a pain to use. Mini laptops are better choices.

Vheck out chuwi tablets