Where does one get these wholesale prices? And I assume that cutting happens at some cost over this?
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.
gemsny.com friendlydiamonds.com lightboxjewelry.com
I found a wide variety of 2-3ct diamonds for $1200-1400 there (round, brillant cut, the "classic" type), which is what a 0.75-1.0ct used to cost
There are literally hundreds of suppliers like that in China/India. Do not pay more than $1000 for a diamond of any size.
You may need to have an account. But there's a ton of interesting and esoteric stuff on 1688.com, so, if you can figure it out, it's worth it.