Oneplus Type C To 3.5mm Adapter (Banggood, Aliexpress: Wire Core: Copper, Product Weight: 3g, Color: Red, Wire Material: Metal+PP+TPE, Cable Plug: 3.5mm jack, Size: 10.5*5.5*90mm, Type C (the best price with coupon)).
Go down and check coupons out. Remember to check price history if it is available. What is the best price?
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. You can get coupon down below.
Link: Banggood product page
1. ($13.20): BG85d5c6
put item in your cart and apply coupon code there after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): TTxBG10, AFfbG10, BGBFAFF2019, BGCITYADS2019, BGVDay10%off, BGAFF10OFF, bGhOnEy10, BGXMI15, BGdragonBoat, BGSS10%SW, BgoFErTaSchInA10, BgcLuBofErtA10, BG20CHARGER, BGMBCBLE, BGHONEY2110, 13f142, BANGGOODSD
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Check out price history chart (for all/most countries) for Oneplus Type C To 3.5mm Adapter. The lowest price was: $3.28.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).