The trade uses a variety of sites for "wholesale" prices. Rapnet is the standard, and they publish the Rapaport Price List. However, it only covers natural diamonds, and rapnet only lists natural. Diamonds generally go for a % discount off the Rap Price List.

Polygon (.net) is the other major listing platform. They include lab diamonds, and most everyone uses them. There are other platforms, but those are the two majors IMHO.

You need to be a member of the trade to sign up AFAIK.

However, I have seen one retail site, Ritani, actually post "wholesale" prices and they seemed to be pretty accurate. They seem to have good prices too. They list their wholesale/markup/etc. Of course, you should buy from a nice local jewelry store, but if you want to buy lab online they are at least great for checking prices.

This is great. Thank you! Ritani is the one I was looking for.