I have just checked coupons. The lowest price I could get is $25.29 for STEM DIY Hot Air Engine Model Educational Toy Kit (in Banggood). Go down and check coupons out. Remember to check price history if it is available. You probably want to know what is the best price?
STEM DIY Hot Air Engine Model Educational Toy Kits
Latest price update (UTC time):
Banggood ($25.29)
Banggood warehouse is located in China. There are no coupons for this product in Banggood. Is it a low price? Maybe there’re no more promotions for this item, because current price is higher than average (which is equal $22.35)
Link: Banggood product page
Price: $25.29
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG589b2e
(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 STEM DIY Hot Air Engine Model Educational Toy Kit.
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)).