I've had success with Craigslist in the past, but can't imagine it's the right place for this price point. Really don't like the idea of getting robbed by eBay and PayPal fees.
PC for 3D.
As much as it pains me the 7,1 just isn't fast enough. An AMD 7950x is twice as fast than the 28 Core Xeon on the V-Ray CPU benchmark. I have the 16 core. On GPU, the 2 6800XT Duos are roughly equivalent to a RTX 4070 on the Redshift render benchmark. That's not bad considering there age (lets forget about the price oof) but Redshift is the only engine you can use them on a Mac. I fear for how much longer Maxon will want to support the Intel platform.