As a rule of thumb, man-made diamonds on average sell for about 10% the cost of natural diamonds. A year ago, they cost about 20%-30% of the price, according to Diamond Hedge.

A natural 2-carat, round-cut diamond with a high-quality color and clarity rating costs about $13,000-14,000, whereas the equivalent lab-grown diamond sells for about $1,000, according to Sompura.

https://www.cbsnews.com/news/cost-natural-lab-diamond/

Edit: That article is a year old. It could be down to 5% now at the rate it dropped already.