You can create price alert here, copy coupons and view price history. Let’s see what best price is ATM.
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 and price update (UTC):
Length (m): 5 Light color: RGB Wattage (W): 24 Voltage: DC12V Power Supply: 12V Features: Color-changing, with Remote Control Certifications: CE, LED Beam Angle: 120 LED Quantity: 300 Color Temperature or Wavelength: RGB, RoHs Width(mm): 8mm Waterproof Rate: IP65 Light Source: 2835 SMD, Festival Lighting
Price history and price alert
Do you need price history chart (for all/most countries) for ZDM 5M 24W Waterproof RGB Light Strip? There we go.
Price records source(s): Gearbest
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)).