1 diamond per $1,000. I have a diamond pick, yes it is damaged. It was bought in buycraft, so $50,000 would be the original price, bit since it's damaged, I will do $45,000, so 45 diamonds I have 33 grass. Multiplying the grass times it's price. 33 times $330 it comes out to $10,890, rounding it to $11,000, so 11 diamonds. I have 64 and 37 iron, making a total of 101 ingots. Multiplying the iron by it's price 101 times $300 it comes out to $30,300, rounding it to $30,000, so 30 diamonds.
Last time I checked it was $50,000, they're kinda hard to get, unless things have changed. I am open to price changes.