The Asus Zenfone 6 will soon be available in the US. B&H has it available for pre-order here's the link but note that the shipping date is yet to be set.
The 64GB model costs $500 and while the phone has a microSD slot, you may want to go up to the version with 128GB storage anyway that's $550. Both versions come with 6GB of RAM. By the way, the card slot can house two SIMs in addition to the microSD card (it's not either-or like with hybrid slots).
The Asus Zenfone 6 is available in Midnight Black and Twilight Silver
Last year, the Zenfone 5z launched at that exact same price point – $500. That's right, unlike Samsung, OnePlus and Apple, Asus didn't increase the price of the phone despite numerous upgrades.
You can read or watch our review of the phone for details, but the gist of it is this: flagship chipset (S855), near-stock Android 9.0 Pie, 48MP main camera that can do selfies (and so can the ultra wide camera), a large 5,000mAh battery with 18W fast charging, all for $500.