As one of its daily deals, B&H Photo-Video offers the ExpoImaging 67mm ExpoCap Digital White Balance Aid for $19.95 with free shipping. That's $40 off and the lowest total price we could find. It attaches to the front of your lens (before shooting) and is used to achieve a more accurate custom white balance setting. Deal ends today.

Of note, it's also available for the same price in 58mm, but you'll incur a $2.99 shipping fee.