Length: 220mm, width: 20mm.
Just check coupons out (with price alert and history). Best price?
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. ($6.34): BGGAL8
2. ($6.34): BGRCParts8
apply it 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): aff7off, rchobbies8, CFadmitad, e2bcea, TTxBG10, BGGEPPart, AFfbG10, BGVDay10%off, BGG2AQ, BGMPB2020, BGAFF10OFF, bGhOnEy10, BGdragonBoat, BGRC902, BgoFErTaSchInA10, Parts8, BgcLuBofErtA10, BGBCSpring1, BGHONEY2110, BGDAVIS, BGRCBC11
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for 5x Banggood 220mm RC Battery Tie Down Strap. The lowest price was: $1.69.
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)).