Just check coupons out (with price alert and history). What is best price?
Battery: 18650 lithium battery(not included), Quantity: 1Set, Material: Metal, Length of welding pen: app.30cm/11.81in, Input line length: app.20cm/7.87in, Color: Red+Blue+Black
Aliexpress
There’re some similar (or not) items on Aliexpress
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 Europe 
. I don’t think there is an active coupon right now – at least in my database. I don’t know if this is a good price – number of records in my database is too low!
Link: Banggood product page
Price: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Old coupons (from the oldest to the newest): BGmini111, BGmini222, BGSTUDENT10, BGdiy12, BGGEE13, BGCuponation10, 13f142, BGHONEY2110, BGf13064, BGfeb901, BG90f9ba, BG6d4c2e, BG6af354, BG1efeb0, MVC8SPRING, tRaDetRaCKeR, BG525f34, hoNEYbGdeAlS, BGJUNEGSG9, BG8ReviTrage, Cuponation9, BGcoupon8off, BGGutscheine, BG00c906, BG8OFFCOUPON, TTBLACK5, BG589b2e
(you can check these old coupons out, but these probably won’t work)
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. China – Portable DIY Mini Spot Welder 18650 ($23.74)
Price history and price alert
There is only one database record (it was for $20.99), so you can’t see price history chart.
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)).