Aliexpress
Click here… to search for UHF Wireless Lavalier Microphone on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (25.41 USD): BGBRPL2
Coupon (25.41 USD): BGHOTSHOP15
(CouponsFromChina.com tip: you should apply the coupon in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BG64465c, 13f142, BGb05d1c, BGBuscape01, BG651551
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for UHF Wireless Lavalier Microphone.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).