Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. You can get coupon down below.
Link: Banggood product page
Coupon (12.31 USD): BG00c906
(CouponsFromChina.com tip: apply it 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): BGRDMIB, aff7off, BGAPPLIANCE, BGaDmITAd, bgchinafest, BGBFCR01, BGCITYADS2019, bGpAnDacHeCk, 2020CNY, BGVDay10%off, BGHOMEAPP, bGhOnEy10, BGAFF7OFF, bgshOOp10, BGHome15%, BGHOMEAPP13, BGHOMEA13, 13f142, BG10OFFAFF, BGwhielabel, BG10OFFAFF1, BANGGOODSD, 00c906
(probably won’t work, but you can try them out)
Price history and price alert
Here is price history (for all/most countries) for Roller Brush Replacement for Dreame V9.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).