Going through Apple's buy site, the previous owner maxed out every single configuration except for storage (2TB not 8TB) and then skimped on purchasing a Magic Trackpad, opting solely for a Magic Mouse 2. If they were going to spend all this, they should have gone all in!
Pretax cost as configured: $51,999 Cost fully maxed out: $53,948
BTW, this refurbished Mac Pro represents a savings of 15% off of $51,999.