fiber optic DP cables are maybe $70 or $80 and work pretty well in my experience.
on the pricier side if you have something with TB support, you can do display and USB over that to a fiber optic TB cable (about $400); this is my current setup for my racked PC in another room to my office, with a TB hub (caldigit TS4) that splits out display and USB.
Any idea if those are thunderbolt 4? Its hard to find any vendor that will state support for 4K144hz through a dock over any sort of extension, right now I am limited to "only" 4K60.
I run a fiber optic display port and can do 4K 120 from 50 feet away. Thunderbolt cables are incredibly expensive I just ran the DisplayPort, an Ethernet, and usb cable - not sure I've seen any TB4 optical cables that are long lengths yet, just the Apple one that's like 6 feet for $200. You can buy Tb3 ones for 400 or so.
I have a 50ft Monoprice SlimRun DisplayPort cable on my 4k 144hz gaming monitor and it works great. However, it's just a DisplayPort cable, not thunderbolt, direct from PC to monitor, no dock. And it cost $170. :/
the only available fiber optic thunderbolt cables I'm aware of right now are from corning, and they are thunderbolt 3. I'm running 5120x1440@120hz through it (and a variety of USB); 4k144hz would be about 35% more bandwidth. Corning lists the cable as supporting 2x4k or 1x5k (presumably both at 60hz); 5k is the same bandwidth as mine, and 2x4k is some what more but less than 4k144hz. Total bandwidth on the cable is 40g and bandwidth needed for 4k144hz is about 32g I believe. can't guarantee it'd work, but 4k120hz probably does?
Dell T7810/5810/5820s can be had second hand for practically nothing and they have fairly modern build specs. They're sized to fit in racks with some basic L shaped rails. They also make great under desk systems as they're whisper quiet.
The downside is that they are 4/5u. But they are a fucktonne quieter than server hardware.
The difficult part is getting the HDMI/DP extenders to work reliably or low latency enough without spending $2k.
Having said all that, Jeff's approach is most likley cheaper, if more fiddly. its certainly neater and more compact.