It's pretty standard to have 8 slots [1] on motherboards and rarely 16 slots [2]
64 gig DDR4 modules cost ~$300 [3] 128 gig DDR4 server modules can cost as little as ~$800 [4]
8x64 = 0.5 TB of DDR4 ram = 8300 = $2,400 16x128 = 1.5 TB of DDR4 ram = 16800 = $12,800
[1] https://www.amazon.com/TRX40-AORUS-PRO-Fins-Array-Motherboar... [2] https://hothardware.com/news/gigabyte-mz31-amd-epyc-7000-mot... [3] https://www.newegg.com/p/pl?N=100007611%20601275379 [4] https://www.newegg.com/p/pl?N=100007952%20601324426