The Samsung Galaxy S4 mini in its dual-SIM incarnation (I9192) is already on sale from multiple online stores in multiple countries.
Amazon US carries the Galaxy S4 mini dual-SIM at $483, but there are only 20 units available at that price and only of the Black Mist color version. If those run out or you prefer White Frost, there are 10 units at $489.
Cells4U undercuts price to $470 for the Black Mist version, cheaper than the single-SIM version.
Then there's Techno Trading House at $515, available only in black. It's $5 more at Negri Electronics, $520, but they have the White Frost version as well. Overseas Electronics have priced the Galaxy S4 mini dual-SIM at $580.