I had the 2019 cheesegrater Mac Pro. 7TB (going from 1 to 8) would cost me $3,000.

So I bought a 4xM2 PCI card, 4 2TB Samsung Pro SSDs for $1,100. And as a result got 6.5GBps versus the onboard 1TB's 5GBps.

Same with memory. 160GB (32 to 192GB) from Apple was also around $3K. OWC sold the exact same memory chips, manufacturer, spec, speed, for $1,000 for 192GB.