I have checked all old coupons and price is 24.29 USD for MZ-501 Infrared Frequency Tester (in Banggood). Go down and check coupons out. Remember to check price history if it is available. Let’s see what best price is ATM.
Latest coupon code price check (UTC time):
Banggood (24.29 USD)
Banggood warehouse is located in China. Price? Well, this price is higher than average price (21.32 USD) There is one coupon right now! Check this out.
Link: Banggood product page
Price without coupon: 26.99 USD
Coupon (24.29 USD): BGAMMT03
(CouponsFromChina.com tip: coupon code has to be applied in shop’s 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): BGSCM11, BG2675f0, BGCRT313, BGCAR639
(you can check these old coupons out, but these probably won’t work)
Aliexpress
Click here… to search for MZ-501 Infrared Frequency Tester on Aliexpress
Here are coupons that you can use.
Price history and price alert
Price history (for all/most countries) for MZ-501 Infrared Frequency Tester is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).