4K TV can run 1080p just fine, so if that is a concern, nothing wrong with some of those cheap 50" smart 4K units out there. I run my 4K TV at 1080p almost exclusively using an HTPC. Only run 4K when I do something with the smart features.
Does it need to be 50" or will 55" do? You might find a more basic TV in the 55" size.
50" seems to be a 'new' size class. I wouldn't have expected to find that size. I was under the impression that 50" and 60" TVs had basically disappeared in favor of the more efficient 55" and 65" TVs they can get out of the current motherglass production sizes for LCDs.
I'm seeing 50" TVs at $200-300, with even a few open box products at BestBuy under $100. I'm sure they are terrible, but still cheap.
I would probably lean towards a TCL TV (2024) if you want it on the cheaper side, and if there is a little room, the Samsung Crystal UHD.
Probably hit up ebay or facebook marketplace and have your pick of older 1080p TVs, maybe even for free.