When I was updating this page, then coupon price was $37.59 for 100A PWM Solar Controller (in Banggood). You can create price alert here, copy coupons and view price history. What is the best price?
Latest price update (UTC time):
Max. PV input power: 750W(12V) / 1500W(24V), Rated voltage: 12/24V, , Max. PV voltage: 50V, Rated current: 40/50/60/100A
Banggood ($37.59)
Banggood warehouse is located in China. Coupons for 100A PWM Solar Controller? Nope, there’re no coupons in Banggood. Is it a reasonable price for this item? From what I can see this price is higher than average price ($20.53).
Link: Banggood product page
Price: $37.59
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG4b5920, BGc03ecf, BGfcfd82, 00c906, BG00c906, ADMITAD2212, 2022ACTIESNL, Tabby20, 2203ActiesNL, tRaDetRaCKeR, 8wEbgaInS5, BG08bdfc, pROMo8cuPoN, BGb305f9, BGRSUNLCD, BG6d2f05, BG1eb57a, BGHUXC060, BG37b1ad, BG4de751, BG7e07bc, BG0b9613, BG589884, BG8OFFCOUPON, TTBLACK5, BG589b2e, BG1d613b, BGET12, BG350285, BG5ef911, BGc9f4ac, BG68ab79, BGe4341d, BGa78dae, BGa61103, BGdb01a1, BG3bca8b, BGET10, BG8FORMULAMX
(these codes were not working in latest coupon update, but you can check them out anyway)
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Here is price history (for all/most countries) for 100A PWM Solar Controller.
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)).