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Green Kid Crafts is $19.95 a month + $4 shipping. Less if you sign up longer. Each Box contains 4-8 Creativity and STEM Science Kits, extension activities, and free online extras.
Use code CYBER18 at checkout and receive Decembers Box free with 3, 6, & 12 month subscriptions.
Also use code BFGET40 and receive 40% off all single boxes in their shop.
You can check out the options here.