Sculpting Woodgrain

Hey guys! Okay, so unfortunately I don't have a budget (No Zbrush=Sad) and only have meshmixer at the moment. What I am wanting to do is add a woodgrain design to Majora's Mask. So that it looks sort of like this.

Attachment 10303

I've figured out how to invert the stencil in Meshmixer by holding CRT (I know, I am practically an expert at 3D sculpting now *major sarcasm, I am very new at this*), but is there any way for me to draw a perfectly straight line, or a line without the bubble look to it using mesh mixer? If not, is there any free 3d sculpting software out there (other than Blender) that you could point me to?

Okay, so I figured out how to make a woodgrain like design using stencils and then the bubble smooth brush. However, now I am having an issue importing the file into MatterControl due to a really high polygon count. I have attempted to reduce the polygon count in Meshmixer by up to 87% (highest I can go before the file starts looking really wonky).

Any suggestions at this point?

Cura slicer typically accepts very high-polygon models.

My suggestion is using Sculptris, it allows for quite advanced sculpting and you can locally reduce polygon counts to fit the geometry.
Use Meshmixer and Meshlab to create watertight and well-triangulated meshes. Sculptris often does not accept a 3D model because of a too high edge per vertex count, so you can either remesh in MM or decimate in ML.

Can you post a picture of your current model?

BTW Meshmixer 3.0 has just been released: http://meshmixer.com/download.html