Terminals like the VT220 were much more expensive because they needed much higher bandwidth analog electronics than conventional TV circuitry (the limit isn't on the B/W tube, it's on the electronics that steer the beam around)

I think there's not much difference in the horizontal/vertical driver circuits.

Here's the (pretty pedestrian and likely not different from a b/w tv) diagram of the horizontal driver for a vt220: https://imgur.com/a/xvq1ukV

The shown MC1391P is, in fact, called a "horizontal TV processor" by Motorola.

I'm sure there's other stuff that made them expensive (CPU, memory, video logic, etc).

Edit: Lol at imgur for marking my screenshot as "erotic" and NSFW.

Awesome find. That said I think the bandwidth issue was less with the semiconductor electronics in that diagram and more with the big analog electronics that actually controlled the gun directly (the box labeled horizontal driver in your image)

Here's the other two boxes:

https://imgur.com/a/yJH9QYu

(Which Imgur also finds erotic and NSFW. Odd)