I’ve searched around and mostly seen people create custom radiator builds attached to their water supply, but that’s beyond my skill level and I’m not sure if linking it directly to the water supply via piping would violate the lease or not. Are there any solutions a bit more DIY that I could take advantage of?
Feasible if you found one at a junk yard, but copper tubing is $20-30 and some fittings makes a tubing idea sub-$100 probably. An AC is about $300, a new radiator without fittings starts at $70 and are built for cars not box fans so it might be more challenging to get to work.
With that being said, environmental, energy, and other contextual concerns might out weigh the cost. A mini-split heat pump is probably the most sane thing to actually install, but that’s a big ask.
You don’t need copper tubing, any tubing that’ll hold water will work. There aren’t going to be high temperatures or pressures. The supply won’t be able to go full blast with poly and hose clamps but it wouldn’t need to. I had a whole plan for this in my head then moved somewhere I didn’t need it and never made it happen.
As for a mini spit, that’s the easiest option if the central is shot, if the layout isn’t complicated. But the place isn’t owned by OP so it’s probably a non starter. They don’t even want to fix what’s there it sounds like.