Aliexpress
Click here… to search for Xiaowei V2 Water Shower Thermometer on Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (22.54 USD): Terence
Coupon (22.54 USD): 2203ActiesNL
(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): BGXVV212, AFfbG10, BGWTR124, BGPQMK2, BGWATE22, BGTHE11, BGWATER88, BGCITYADS2019, BGBGHFRI15, BGBAPOHG, BGHNWTE, BGHOMEG12, BG303cv, BGAFF10OFF, BGAPR19, bGhOnEy10, BGdragonBoat, bgshOOp10, BGHome15%, BGHOMEA15%, BgcLuBofErtA10, BGZASKDK48, BGBTJU20214, 13f142, BGBTJU74, BGBTJU90, BGCuponation10, BGMA1002, BGAP1205, BG10OFFAFF, BGwhielabel, BGJUY285, BG10OFFAFF1, BANGGOODSD, BGAlerabat1, Tabby20
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Price history (for all/most countries) for Xiaowei V2 Water Shower Thermometer is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).