I got lucky and picked up a second hand HP-7475A for $50 about five years ago. It's the GPIB version, not native RS-232, so I also had to find a way to connect it to a modern PC. Ended up going with a GPIB<->USB adapter from AliExpress (about 10x cheaper than one from Prologix) to plug it into an RPi, which I can use to send HPGL files to get plotted.

Also got a friend to hack away a chunk of the plastic casing with a circular saw so I could use pen adapters for modern Sharpie and Stabilo markers, which are much easier and cheaper to acquire than old format plotter pens.

I’ve always wanted to get one of these working, but they’re rare, and heavy! That makes shipping expensive.