A DC of diamonds would go for 414k @ 120r/diamond I don't know what you mean by a school of diamonds though ;-;
Well if each individual diamond goes for 100r then 9 Diamonds to make up a block would be 900r. Hope this helps.
I know this is a week old but it hasn't been answered so... If my maths is correct a dc of diamond blocks, with each diamond priced at 100r, would be equal to exactly 3,110,400r