SPF 3500-80A.
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. There is one coupon available! Pretty cool, huh?
Link: Banggood product page
1. ($908.03): BG589b2e
this code has to be applied 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): Terence, BG68ef53, Tabby20, 2203ActiesNL, BG1efeb0, MVC8SPRING, 8BGwbg2204, Cuponation9, 9OFFSUMMER
(there’s a little possibility that old coupon will work)
Price history and price alert
Check out price history chart (for all/most countries) for Growatt Hybr1d SPF 3500-80A Solar Inverter. The lowest price was: $714.14.
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)).