Connecting interface: 3.5mm, Type-C, Driver unit: 57mm, Frequency response: 15~25000Hz, Impedance: 16ohms, Sensitivity: 116dB, Bluetooth Version: V4.2, Battery Capacity(mAh): Built-in 650mAh Li-ion Battery.
Just check coupons out (with price alert and history). What is 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 code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($57.74): AFfbG10
2. ($57.74): EARSP11
3. ($59.16): 7d18f7
apply code in your basket (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): d4de0b, TTxBG10, BG3CSUM, BGBFAFF2019, BGCITYADS2019, BGVDay10%off
(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
Price history (for all/most countries) for Bluedio T4 Bluetooth Headphones is here. The lowest price was: $25.99.
Price records source(s): Gearbest, 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)).