When I was updating this page, then coupon price was $26.99 for 4000mAh 150PSI Portable Car Air Inflator (in Banggood). You can create price alert here, copy coupons and view price history. Best price?
4000mah 150PSI Digital Display Portable Car Air Inflator Motorcycles Bicycle Tyre Wired Inflatable Pump
Latest coupon and price update (UTC):
Banggood ($26.99)
Banggood warehouse is located in China. I couldn’t find any coupon for this product on latest product update. Is it good price? Looks like a good price to me (average is $27.49).
Link: Banggood product page
Price: $26.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG4a2ae1, BGLMQ15, BGSCM11, BGAMMT03
(these coupons are old, so probably won’t work)
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Price history (for all/most countries) for 4000mAh 150PSI Portable Car Air Inflator is here.
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)).