In the past when I had two monitors (one of which was a U2711) on a cheap desk I think I just added a bit of wood top/bottom to help spread the load. Not exactly a looker but have since made a desk shelf so that would be hidden if I needed to do it again I guess.
My desk is a solid wood butchers block worktop from IKEA (at least 14 years old), bought separate adjustable legs to go with it. It is rock solid and has taken a lot of abuse over the years.
Yeah I considered upgrading the desktops themselves with either kitchen worktops/something else but figured I can always do that at a later stage, limited funds should be put elsewhere for now
Chairs - if you don't want to splash on a miller, then the IKEA Markus is very well regarded, especially if you're taller (I'm 6' and its perfect for me, although I did some work to alter the arm rests. Monitors - mount them to the wall on a decent gas powered arm and then you can use any standing desk you like.
Given the limited budget I can't recommend facebook marketplace enough. I picked up an aeron not too long ago for sub £200 I also got a second hand flexispot frame for £70 then put a solid oak top on it for another £140ish Finally rounded it off with a second hand Ergotron MX for £15, which handles my 34 ultrawide just fine Bargains are out there, be patient!
I think we've tried the Markus but may be worth another look. Already potentially considering swapping desks between rooms so don't want anything permanent right now Yeah will keep an eye out, no crazy rush but I'd rather just get something, and main reason for not wanting to spend too much is no garuantee of it actually solving the problem, if it would 100% then we'd already have bought whatever was required and worked out how to afford it later