[juped]

Threadripper has its own socket type so I'd go with a cheaper or older one of those. Though I think third-gen threadripper is another socket entirely

[junar]

The problem is that Threadripper mobos are expensive, and as you said, 3000-series Threadripper don't use the same socket as earlier Threadrippers. Under $1000, it's better to optimize the budget for GPU and RAM, and avoid spending too much on the CPU+mobo. You can always upgrade the latter two together if needed.