How do you own inventor? Is it a student license? If so, you can get autocad 2016 and inventor hsm (has cam software built in) 2016 for free. Otherwise it would probably be a similar cost to inventor. There are many other 2d cad programs and I think many of them will export to a .dxf file, but I don’t know which ones are good. As a student I am always up to date with the latest autodesk products.