Aliexpress
Click here… to search for 6x Lead Free Solder Iron Tips 900M-T on Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (4.58 USD): BGherra
Coupon (4.58 USD): BGWELDTOOL
(CouponsFromChina.com tip: you should apply the coupon in your 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): elec, TOOLS15, AFfbG10, 502C6B, BGBFAFF2019, BGCITYADS2019, BGMPB2020, bGhOnEy10, BGTool15, BGRUS15
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Price history (for all/most countries) for 6x Lead Free Solder Iron Tips 900M-T is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).