There's an 8K 10.1" Mono LCD (SMP1018K13A0) and matching UV source that is £310 total and has a lot of good stuff:

• Square pixels of 28.5um, compared to 50um for the 8.9" 4K
• 10% transmittance, which is almost double the 5.4% of the 8.9" 4K
• Long edge is 218.88mm, which I believe is only a few millimetres longer than typical A4 scanner sensors (8.5" = 215.9mm)

This is only held back by its low availability:

I'd like to have something like a 215 x 430 mm build area so that it was also possible to print half of an A3 poster.