It appears that some rare cells are only available for 1 diamonds. Mudflow cells used to be availalbe for silver, but recently I saw only offers for diamonds, while only breedable rare monsters were offered for gold I think.
@Community-Managers, is this intentional? This would once again be a slap in the face of newer players, since "older" players will have bought all these cells for gold, so it would be unfair to change the price to diamonds.