[No Pattern] Can anyone explain how this would be sewn? Sewing Machines Parts and Sales in Los Angeles

So, I have found a vintage style sweetheart dress that I am in love with, however, I cannot justify $90.00 for a dress and I certainly do not wear a small.
[ https://pinupdresses.com/#!/New-Retro-Black-Halter-Full-Skirt-Dress/p/49379219/category=13004703 ]

I am familiar with how to drape and sew a sweetheart neckline bodice, however with this dress I don’t see any visible seams.
It appears that the dress only has a couple of darts over the breasts (princess line darts I think they’re called?) and a bow in the back to help cinch the waist some.

I really enjoy the seamless look, but I have no idea how to go about draping something like this or even sewing something like this.

Can anyone explain this please?

Thanks!