If you could do the same job on a fleet of 8-16GB servers.. you can get a lot more CPU for a lot less dollars. Depends if you really need everything on 1 machine or not (as of course nothing will beat same machine in memory locality)
Not true, 8x16GB costs as much as 1x256 on Amazon. The issue here is that Amazon is hilariously expensive in general. Hetzner will rent you a 256GB server for €460 per month. Or you can buy one from Dell for $5000. These are not high numbers, in 1990 you paid more than that for a "cheap" home computer. For the price of a floppy drive back then you can now get a 32GB server.
these are on-demand prices. pre-pay, or use a term discount, and its cheaper.
Build it yourself: You can build a Dell or similar on a 2-Xeon-proc (E5 series), your main limit is getting good prices on 16x 32GB DIMMS. But lets say you can buy the RAM for ~$6500, then its just dependent on the rest of your kit, lets say $10,000 flat for the whole server. $277.77/mo over 36 months, but you still need network infrastructure, and you might want a new one in 12 months, but you get the general idea.
and fwiw, costs at amazon will scale linearly with resources. the 1 beefy box with 256GB RAM box costs about as much as 16 boxes with 16GB of RAM each.