Just check coupons out (with price alert and history). Best price?
Heating Temperature: 50 degrees, Leg Sole: 21.5-30cm, Material: Cotton, Height: 19-37cm, Power: 2x AA batteries (Not include), Color: Black, Size: M, Heating Parts: Toe back
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. I found coupon for you. Check this out.
Link: Banggood product page
1. ($14.39): BGAMMT03
this code has to be applied in your 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/5cd
Old coupons (from the oldest to the newest): BGa5c643, BGSCM75, BG589b2e, BGSCM11, BGCAR639
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for 2pcs Electric Heated Hot Socks.
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)).