I have checked all old coupons and price is $12.99 for Electromagnetic DIY Electronic Kit Coil Booster Circuit Board (in Banggood). Basically copy coupon, view price history or create e-mail price alert. Do you want to know what the best price is?
Electromagnetic DIY Electronic Kit Long-range Projectile High-voltage Coil Booster Circuit Board Production Welding Electronic Science Experiment – Parts + shell
Latest coupon code price check (UTC time):
Banggood ($12.99)
Banggood warehouse is located in China. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood. Is it expensive? Hmmm, price is higher than average (which is $10.08 right now), so better set price alert down below…
Link: Banggood product page
Price: $12.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
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 Electromagnetic DIY Electronic Kit Coil Booster Circuit Board.
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)).