Aliexpress
Click here… to search for OnePlus 7T Pro 8/256GB Blue on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in Hong Kong.
Link: Banggood product page
Coupon (629.99 USD): bgshOOp10
Coupon (692.99 USD): Email5
(CouponsFromChina.com tip: apply code in your basket (cart) after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGOP7TP256, od7off, BGOP7TPROPL, BGOP7TP, BGWKOP7TP, BGD11OP7TP, BGD11AOP7TP, BG11OP7TP256, BGBFAFF2019, BG3COP7TP, BGAOP7TP, BG7TPROPL, BGNAOP7TP, BGCITYADS2019, BGBF7TP8256, BG12OP7TP, BGUOP7TP, BGD12OP7TP, BG1OP7TP, BG1DOP7TP, BG2OP7TP, BG6187TP, BGOP7TPJ1, BG7TPJ12, BGOP7TSP
(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 OnePlus 7T Pro 8/256GB Blue is here.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).