Third one looks crysis inspired.
It doesn't look as precise as the other two though. The shading doesn't quite fit the shapes sometimes. Like in the back tubing, there is only shading horizontally, but not along the segments.
The first is my favorite, I think, but the patterns are repetitive. All corners, right?
It's a bit bland. The back mixes together. Again, some variety would help a lot. Maybe different shading styles.
I have absolutely no idea of head prices now, but I would've said 20-30k. So would that be 10-15k now, since 5k=$1, instead of 10k?
2nd is nice. way different from the other two, so I can't really say if it's better or not. Just depends on the buyer's tastes, I guess. The mouth is well done, but the eyes and tribals are pretty generic looking.
Are these in 512x512 or 256x256?