TomTop offers the Tomshine 12-watt E27 12-LED Plant Grow Light Bulb for $17.49. Coupon code "LCXL1483" cuts it to $11.89. With free shipping, that's the lowest price we could find by a buck. This IP44 waterproof bulb features three 460nm blue LEDs, nine 630nm and 660nm red LEDs, and an aluminum heat sink.

Also available is the 24-watt version for $13.59 with free shipping via the above coupon. That's also the best deal we could find by a buck.

Note: These items ship from China and require two to five weeks for shipping. The countdown timer on the product page does not reflect an actual expiration time and resets daily.