For the same performance, one could even go about 50% cheaper with 16 channel ddr4 + a rtx3090 for prompt processing.

But still, even for mid level projects API is orders of magnitude cheaper, since you don't need to set it up and maintain it.

The memory bandwidth of the 2x RTX Pro 6000 Blackwell setup will be 10x higher, which should have an equivalent effect on the generated tokens per second.