Dual SIM variants of the Galaxy S8 and the Galaxy S8 Plus are currently quite affordable on eBay, well, at least compared to its original price points. The Galaxy S8 is currently priced at $579.99, while the Galaxy S8 Plus costs $665.99. Do keep in mind that these two phones are not being sold directly by Samsung, though, this is eBay we're talking about after all. Despite that, however, a seller who had listed these two devices has a great rating on eBay, so there should not be any problems in that regard.
Do keep in mind that these are international variants of the Galaxy S8 and the Galaxy S8 Plus which come with support for two SIM card slots. These two phones will work with basically any GSM network worldwide, but if you're currently tied to a CDMA carrier, well, you're out of luck. Both of these phones are made out of metal and glass, and both of them ship with Samsung's Infinity display, and have really thin bezels. Samsung's Exynos 8895 SoC fuels both devices, and they both come with 4GB of RAM on the inside.
In any case if you opt to purchase the Galaxy S8, you'll save up $145, while the Galaxy S8 Plus purchase will save you $159 compared to its original price. Both devices are currently available in both Gold and Gray color variants, and shipping is free within the US, and this is a limited time offer, as quantities are limited, so hurry up if you're interested.