My source is the 2 volume The Crown Jewels of 1998, which I used before in this thread.
Queen Mary's Crown was made by Garrard & Company with nearly 2,200 diamonds for her coronation in 1911. Today the crown on display has rock crystal replicas of the Koh-i-nûr and Cullinans III and IV. The Koh-i-nûr was set on the front cross, Cullinan IV in the front centre of the band, and Cullinan III in the cross paty above the monde. I don't think the Koh-i-nûr in 1911 included its "oval frame of small rose diamonds". That frame was included for Queen Alexandra's, and it's replica was added to Queen Mary's in 1914 with the replica Koh-i-nûr . For the 1937 coronation, the Koh-i-nûr was replaced by Cullinan V in its "delicate platinum and diamond surround". I have not found what was used to replace Cullinan IV on the band (see pic).
"Garrard received payment for the Crown from Queen Mary's Privy Purse; no record of its materials and cost is available, though the Queen probably followed the example of Queen Adelaide and Queen Alexandra in using stones broken out of family jewellery. The majority of stones are old-fashioned cushion-cuts." Queen Mary did not meet the cost of the work done in 1914.