Target YMMV: Hori Nintendo Switch Left D-Pad Controller (Handheld only) $9.98
Some Targets have this replacement left Joycon with a D-pad on clearance discounted from $19.99. $9.98 seems to be the lowest, while $13.98 is more common. There's also a 10% off cartwheel coupon in the Target app.
Note that this is for handheld mode attached to the Switch only. It will not operate wirelessly. The minus and screenshot buttons are also soft rubber instead of hard plastic and there is no rumble.