Alpha vs non-alpha unlit shaders

I am developing a 2D iOS game, and am using two of the unlit shaders (Unlit and AlphaSelfIllum) that I found on the Owlchemy Labs site: http://owlchemylabs.com/content

I'm wondering how much of a performance difference there is between an alpha-blended shader and an opaque one? When spritesheeting textures, is it worth an extra draw call to put textures that don't need to have alpha on a material with a non-alpha shader? Or is the exra draw call more expensive?