Depends on the use case, as for hardware h265 codecs a rtx 5070 Ti works just as well as the rtx 6000 gpu. Legacy GPU don't support modern codecs, but modern Intel chips have h265 HDR hardware support. Lower <16GB VRAM GPU are not really useful for "AI" model labs, so are often far more economical for rendering media.
One metric that isn't considered is VRAM, as some rendering pipelines still rely on composited baked-scenes to reduce each areas memory requirements.
In general, the $/performance unit will depend on what you are doing, but there is 1 more thing to consider... Old GPU use mystery binary BLOB drivers no longer maintained on modern kernels. You might get the software to work with a legacy Windows GPU driver, but the key takeaway concept here is "might". =3