STL files for Visual Mill Version 3

I am interested in trying the free Visual Mill Version3.

As I understand things it will only input STL files and not DXF.

What low cost software CAD software are people using to create STL
files? Same question for converters DXF -> STL.

I have TurboCad V7 standard which will output DXF but not as far as
I know STL.

Thanks