NVIDIA GeForce MX150 2GB GDDR5, RAM: 8GB DDR4 Large Memory for High-speed Response, Hard Disk: 256GB PCle SSD for Quick Read Speed, Intel Core i5-8250U quad core 2.5GHz.
Basically copy coupon, view price history or create e-mail price alert. 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. ($619.99): BGPL13th02
2. ($619.99): BGXMAA2
3. ($629.99): BGPUREAIE
4. ($629.99): BGXMA4
5. ($780.19): affiliate6
6. ($809.99): Wholesale20
paste coupon code in your cart and click Apply 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): 10I5150, 1B0GMX8, 1B1G1LAP1, SPL1A1P1, 1B1G142464, 1B1G13064, B12G0364, 1225CAR, B12G0664, BG190664, 19BG2642, BG1912642, BG312642, BG382642, TECH8%, BG212642, BG252642, BG3292642, PCMF2642, bglower2464, BG51464, bg64531, BGXM3286, BGMX1524, aff7off, BGXM32464, BGJL3D01, BGAIRXMPL, BGXMGL79, BGXMGL17, BGXMGL23, BGAIR133, BGXM1333, BGESAIR133, BGXMAL133, BGXM133250, BGXMA464, BGXMA4641, BGXMA3
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Price history (for all/most countries) for Xiaomi Mi Notebook Air 13.3 8/256GB i5-8250U MX150 DARK is here. The lowest price was: $619.99.
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)).