[reaperducer]

With modern electronics and displays, could something like a model 100 be made that could run for hundreds or even thousands of hours on 4 AA batteries?

The biggest problem is the screen. People aren't going to tolerate a 40x8 (320px x 64px) screen with no backlight and limited contrast.

Putting a modern screen on it is going to eat power beyond your budget.

The M100's refresh rate wasn't great, so replacing the LCD with an e-ink display would be comparable, except it would far more expensive.