Latest update shows that 9V-36V Digital LCD 50-9999RPM costs 23.62 USD (in Banggood). Basically copy coupon, view price history or create e-mail price alert. Best price?
Latest coupon and price update (UTC):
Banggood (23.62 USD)
Banggood warehouse is located in China. Well, is it a good price anyway? Hmmm, price is higher than average (which is 11.13 USD right now), so better set price alert down below… We have found one coupon for this product!
Link: Banggood product page
Price without coupon: 26.24 USD
Coupon (23.62 USD): BGAMMT03
(CouponsFromChina.com tip: just apply this code 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): tRaDetRaCKeR, BGAUTO22, BGdcbfa8, BG00c906, Cuponation9, 9OFFSUMMER, BGSCM75, BG589b2e, BGSCM11, BGCAR639
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Aliexpress
Click here… to search for 12V 24V 9V-36V Digital LCD 50-9999RPM Tachometer on Aliexpress
Here are coupons that you can use.
Price history and price alert
Here is price history (for all/most countries) for 12V 24V 9V-36V Digital LCD 50-9999RPM Tachometer.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).