You can get commodity x86 server with 12TB RAM and 224 cores.
https://www.supermicro.com/products/system/7U/7088/SYS-7088B...
It depends what is meant by "commodity" I guess.
The largest server AWS offers is only 64 physical cores (128 logical) and less than 4 TB RAM.
Quad socket R1 (LGA 2011) supports Intel® Xeon® processor E7-8800 v4/v3, E7-4800 v4/v3 family (up to 24-Core)
Up to 12TB DDR4 (128GB 3DS LRDIMM); 96x DIMM slots (8x memory module boards: X10QBi-MEM2)
AFAIK the latest Skylake Xeons ("Scalable" - Platinum/Gold/Silver/Bronze) have regressed to 1.5TB support, see https://ark.intel.com/products/93794/Intel-Xeon-Processor-E7... http://www.colfax-intl.com/nd/downloads/Intel-Xeon-Scalable-... corroborated by https://ark.intel.com/products/120502/Intel-Xeon-Platinum-81...
Since a single 128GB stick costs about 2900 USD, 96 of them will run to ~280 000 USD plus the server so it's likely to be above 300 000K.
If you want to go with 6TB "only" then it's a lot, lot cheaper as 64GB RDIMM sticks can be had below 700 USD. The end result might cost closer to a third of the 12TB server than half of it.
RAM prices comparison: https://memory.net/memory-prices/
https://www.supermicro.com/products/system/7U/7089/SYS-7089P...
Server itself is might only be $25k but those 224 cores could add another $90k, so the total would be close to $400k.
The previous-gen version, SYS-7088B-TR4FT (link in my comment upthread), has 192 DIMM slots, so if you don't need CPU horsepower, you cn get the lower-density modules and still have 12TB (or the max of 24TB for the price premium!).
Even previous gen, if 12TiB main memory is your goal (NUMA concerns aside), it's probably worth going for the 8S system instead of the 4S one, since that's a savings of $144k, and 8 slower/fewer-core CPUs might even be cheaper than 4 that have twice the performance.