Power requirements: dc9v-24v, bluetooth distance: at least 12 meters (barrier free), Output power: 50W + 50W, bluetooth protocol: 5.0, Type: Digital Amplifier, Product size: 110mmx90mmx50mm/4.3inx1.5inx1.9in, Function type: 2.0 stereo, Color: Black / Silver, Net weight: 160g.
Just check coupons out (with price alert and history). Let’s see what best price is ATM.
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. I’m afraid that there’s no working coupon in Banggood.
Link: Banggood product page
Price: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): BG4BW25, BGLOAC1, 13f142, BGa0b145, BGBRPL2, BG53e9c8, BGAlerabatKL, BGd173b4, BGAudioVideo, BGAUDIO, BG9ba0e8, BG1b5830, BGAudio3
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Price history (for all/most countries) for HiFi Mini Digital Amplifier Bluetooth 5.0 is here. The lowest price was: $16.99.
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)).