The new Samsung Galaxy S9 and S9+ already came out earlier this year, but if you're not overly enticed by Samsung's new flagships or prefer to save a few hundred dollars and get something that's slightly less cutting-edge, you might consider purchasing last year's Galaxy S8 or S8+. If that sounds like you, you'll be pleased to know there are a few deals on eBay that'll net you an unlocked S8 or S8+ (either new or refurbished) starting at just $411.84.
You can find a seller refurbished Galaxy S8 and S8+ on this seller's page, with plenty of options and configurations to choose from. Right now, you can find a Verizon Galaxy S8 (SM-G950U) in "Excellent" condition for as low as $411.84 ($188.15 off its current price of $599.99) and a GSM unlocked S8+ (SM-G955U), also in "Excellent" condition, for $483.84 ($206.15 off the current price of $689.99). Some colors are only available for certain carriers, so play around with the options.
If buying refurbished isn't for you or if you need a dual-SIM model of either phone, you can also find a factory unlocked dual-SIM Galaxy S8 (SM-G950FD) for $533.99 ($66 off) and a factory unlocked dual-SIM Galaxy S8+ (SM-G955FD) for $584.99 ($105 off).
Both these deals are slightly better than the best one we'd seen so far, though admittedly not by a lot. Check out the source links below if you're interested.