Rated voltage: DC 5V charging voltage, Voltage: 3.7V, Battery capacity: 700mAh, Rated power: 2.5W, Product size: 141 * 62 * 52mm, Emitting color: Bluish violet, Type: UV germicidal Disinfection lamp, Product model: Z2.5D8Y-01 white, Z2.5D8Y-02 black.
Basically copy coupon, view price history or create e-mail price alert. Let’s see what best price is ATM.
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. 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
1. ($35.96): 8Couponsde
2. ($35.96): MVC8SPRING
3. ($36.74): BG00c906
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 and https://couponsfromchina.com/short/i1u
Old coupons (from the oldest to the newest): 0e7f33, BGLIGHT2020, BGXDDJP, bGhOnEy10, bgshOOp10, BGXMDL, BgcLuBofErtA10, BGAFF10OFF, BGCuponation10, 13f142, BG10OFFAFF, BGwhielabel, BGLIG12, BG10OFFAFF1, BGd0b05d, 00c906, ADMITAD2212, 2022ACTIESNL, Terence, BGLED2203
(these coupons are old, so probably won’t work)
Price history and price alert
Price history (for all/most countries) for Xiaomi Xiaoda Sterilization Desk Lamp is here. The lowest price was: $16.99.
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)).