Just make sure that you get something with really good shaders and not just textures.  Many free packages don't have good shaders.  If I remember right, V4 Francesca (or Francisca; I don't remember) on ShareCG has really nice shaders and textures.  She has a medium skin tone.  But, if you're serious about this, I think $5-$20 is a logical amount to spend to invest in some decent textures and shaders.  I do agree that the morph is also important, so look for a package with a realistic (or interesting) face as well.

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