Convert *.STL file of human head to NURBS, convert to *.STEP files

I have *.stl models of the human head ( includes skull the skull have 4 components and, skin, and only orbital fat and eye). I can convert it to solid part, but it is hard to modify in Solidworks since the part is complicated. I need very minor modification to mesh as well, cover two small holes in the skull ( it probably take less than 10 min for expert) I would like someone to convert it to NURBS, in (*stp ) which I could modify using SolidWorks ( I want to get rid of triangles and have it as NURBS). I want a smooth surface without all the subdivision created by the mesh. **Important Notes: -The maximum budget is 50$ so please don't bid more. - You need to have experience working with complex mesh file. - You need to have experience converting mesh to NURBS