Woot offers Apple USB-C to 3.5 mm Headphone Jack Adapter for $6.99 (orig. $19) free shipping with Amazon Prime.

Product Description:
The USB-C to 3.5 mm Headphone Jack Adapter lets you connect devices thatuse a standard 3.5 mm audio plug — like headphones or speakers — toyour USB-C devices.

• The USB-C to 3.5mm Headphone Jack Adapter lets you connect devicesthat use a standard 3.5mm audio plug - like headphones or speakers - toyour USB-C devices
• Works with all devices that have a USB-C connector and support iOS 10 or later.
• Compatible with iMac, MacBook Air, MacBook Pro and Mac mini featuring a USB-C port