Color Gray, Charging Method USB Charging (USB Cable Length 120cm), Complete Set Size 33*18*3.5cm/12.99*7.08*1.37in, Battery 5000mAh, Power 7.5W, Material ABS+ Diving Material, Heating Gear 3 Gears (45°C/50°C/60°C), Weight 300g.
Basically copy coupon, view price history or create e-mail price alert. Do you want to know what the best price is?
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 and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($27.99): BGa66594
2. ($38.21): Cuponation9
3. ($38.63): BG8ReviTrage
just apply this code in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): BG7ac30c, BGHB218, BG2d31bc, BG72fff5, tRaDetRaCKeR, BG3fc23d, BGHECARE1, BGMUML65, BG8516c5, BG724b00, BG4ee866, BGb808ae, BG48681b
(there’s a little possibility that old coupon will work)
Price history and price alert
Here is price history (for all/most countries) for Wireless Far Infrared Heated Massage Knee Pad. The lowest price was: $24.99.
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)).