This app is great and provide you a good indication if you understand how to work with it.
Prices are the maximum you should pay for a perfect diamond. Then, there are discount drivers that will affect how much you would pay below this price.
For example, if a diamond have strong fluorescence or bad make, it can drop the price down to 30% below the quoted price.
The education section is taken from GIA website and is oriented to consumers who have no clue about diamonds. It does not presume to make you a trained gemologist, but it does the job explaining about the four cs.
Jake1968 about iDiamonds (Estimated Retail Diamond Price for Consumers)