If you are in the market for a Galaxy S9 in the US, you should check this deal: dual SIM Galaxy S9 for $640. An eBay seller with over 99% positive feedback is offering the promo.
The model on offer is an international one that comes with Exynos SoC instead of the Snapdragon chipset that you find in US Galaxy S9 units. It is only compatible with GSM carriers, and offers 128GB storage. The only available color option is black, though.