Best place to purchase lab grown diamond

I need to replace my damaged ring, which I bought through Lauren B and was a moissanite stone. After some research, I've decided to upgrade to a lab grown diamond. However, I've noticed that the lab grown diamonds on Lauren B's website are more expensive compared to other websites. Does anyone have any insight into why this might be the case. Insurance will pay me out, so I do not need to purchase through them again, but I’m so very curious.