Ok, so some things to know.
The PC-98 outputs a resolution of 640x400 (16:10 aspect ratio) and requires a monitor that supports a (horizontal) frequency of 24kHz.
However, most monitors do not support frequencies this low, with the lowest they support typically being 31kHz.
Monitors that were made for the PC-98 obviously work, but there are also a decent amount of older monitors that will
run at 24Khz and work with the PC-98, even though the manual/specifications list 31kHz as the lowest it supports.
These are great options because they can often be had for much cheaper than trying to get an authentic monitor.
Unfortunately it has been hard for me to find information on which monitors work, so I decided to make this page
listing what I have found, for myself, and any one else that might be interested.
Obiously these monitors will work. These include monitors like the KD series.
One interesting series is the PC-TV series.
These monitors are designed to work as TVs and PC monitors.
They have many inputs, and are great as displays for retro games as well as PCs.
Because of that though, ones in good condition can be pretty pricey.
I'm going to list some LCD monitors here that should work with the PC-98, even though they don't officially
support 24kHz.
Most of this information was gathered from here,
by a fellow going by the name Takerun, so credit to him.
The site is in Japanese but has some images and more information than I will have, so check it out if you are interested.
Also, please note, these monitors do not officially support 24kHz, so it is possible that there may be different
hardware within the same model that may not work, ie if they changed screens or components for later models.
I will add more monitors as I find them, but generally this will just be monitors that I am interested in.
This is a 17 inch square (1:1?) monitor with a resolution of up to 1280x1024.
It allows for a fixed aspect ratio that supports 640x400 output from the PC-98 so there is no stretching.
Has issues displaying 31kHz apparently.
20 inch 1600x1200 4:3 monitor.
Displays 640x400 24kHz quite well. In fact, it officially supports 24kHz!
Likely harder to find than the RDT172M and so probably a bit more expensive.
I only see 3 auctions within the last 6 months on Yahoo Auctions at the time of writing this.
A 25.5 inch, 1920×1200 monitor. This monitor is 16:10 so it is natively the same aspect ratio as the PC-98.
I'm not 100% sure if it works with the PC-98. The writer says he tested it on the PC-386GE and it looked great,
but that is a PC-98 clone by Epson and not a PC-98 by NEC.
Though if the clone works I would figure the PC-98 would too.
However, when he tested 24kHz on his X1turboZ (a Sharp machine), it supposedly didn't display properly.