I estimated the cluster to achieve this was ~$3-4k per-hour. I am thinking there is a typo on the r8g.16xlarge and they are actually r8gd.16xlarge (notice the d) which comes with directly attached nvme disks.
It felt rude to take so many r8gd instances away from our customers who really love those (and i8g and i8ge).
We used r8g.16xlarge instances with EBS disks, no nvmes