https://www.lenovo.com/us/en/p/laptops/thinkpad/thinkpadx1/thinkpad-x1-fold/len101t0047 This & some window tiling

Asus zenbook duo. Probably the best of this type.

I really wish MS would have put these people in charge of shit. - https://www.youtube.com/watch?v=pFQWc79TYcU

I connect an external monitor to my tablet. It’s not a portable setup though.

The Microsoft Surface Duo 2 is the only one I know that does that. Yes Microsoft makes Android devices.

Alternatively, two tablets and a little bit of duct-tape would also achieve a similar result.

Lenovo has the "yoga book" which is a dual screen laptop with stylus support but it's pretty expensive (discounted to $1599 on their website at the time of writing) although they look like they do offer a student discount

https://www.lenovo.com/us/en/p/laptops/yoga/yoga-2-in-1-series/lenovo-yoga-book-9i-gen-9-13-inch-intel/83ff0001us

ASUS Zenbook Duo is a dual-screened laptop. It might be bigger than you are looking for, but it is exactly that form factor.

I’d look to see if your tablet could drive a USB-C monitor for the video/textbook screen. You can pick up pretty good 14” ones from HP and Dell for like $130.

You could use a Samsung Tablet with Dex that supports the Samsung pen, and connect a portable monitor to it. There are decent portable monitors under $100, certainly enough for watching lectures. The two displays wouldn't be connected by a hinge but by a usb C cable. In return the display sizes and orientations wouldn't have to be the same. If the portable monitor doesn't support touch, I recommend throwing a bluetooth mouse into the mix to make navigation easier.

Edit: I could also confirm it working with an iPad (Air, M1) and said portable display. But iOS forces you to connect a bluetooth mouse and keyboard to be able to extend the display instead of mirroring it.

LG v60 in phone form factor. They should have made a sequel and a tablet. Awesome device.

I have a Remarkable Paper Pro. I use it for notes, organization, reading books, etc. I love it.

The new Supernote is also a compelling option.

The ePaper display means I rarely have to worry about battery and the pen feeling is MILES better than any LCD I've ever tried.

My files all sync to my laptop and my phone, and it is way more comfortable to write on than a double screen device because I can have my 'pad' in letter orientation and my hand doesn't run into the screen which can happen on the double screen devices.

It's also fantastic for taking notes in meetings because I don't have a laptop between me and the others and I don't get distracted by notifications. It's also light enough to disappear into my bag next to my laptop.

So, I thought I bought this... It's a kickstarter called the OKpad. Word of warning: it is not OK.Run screaming! The e-ink bit? No backlight, no rotation, no keyboard. The LCD bit? Meh. Takes a day and a half to charge, runs out in three or four hours. Runs out while plugged in! Four releases back on Android. So, yeah, OKpad sucks.

You could put an external display on your tablet. Support is hit or miss, but possible.

Would a laptop with a touchscreen not work for you?

You can make it right now, get two tablets and a piece of software called unified remote, done

There are some devices that do this, but as you've already noted, they're crazy expensive. There's cheap(er) ways to accomplish the same thing, though.

Assuming you don't need to do any heavy-duty computing on either screen, you could probably get away with a very cheap laptop for the primary display, and something like a Wacom display tablet for the touchscreen element. I'm not sure how compatible such touchscreen displays are with Chromebooks, but most Chromebooks easily have Linux installed on them, which I'd imagine has much better support. Or pretty much any low-spec Windows laptop would also work just fine.

You could probably get away with a decent setup like this for the $500-600 range. The tablet could rest over the keyboard of the laptop, or if you're clever with drafting and have access to a 3D printer, you could probably easily print yourself a mount of some sort to secure the touch display over the laptop keyboard to avoid pressing keys and give it a more intentional design. I don't know how well using an on-screen keyboard would feel, so something modular like this, where you could easily expose the real keyboard without too much fuss, may be a good route to take.

The only ones I know about are the ones with folding displays.