Apple will let you add 256GB of RAM to an iMac Pro for $5,200
theverge.com
theverge.com
Anyway, now there is a great solution for this issue and it is only $5200.
Btw the link should be changed from news.google.com to theverge.com
The prices start at 6.84€ per GB (versus 25€ per GB at Apple)