Not at 24bpp, but maybe at 8bpp?

Indeed. So far as I recall I had a greyscale monitor that couldn't do more than 800x600. I think it was a 486sx and I probably still had a 32GB MFM hard disk at that point so it was a very underwhelming machine.

I think 1MB of RAM in a simm was about £100 at that point, but it's been a while!

Yes. Also X in 1bpp was not even rare (e.g. Sun bwtwo).