Eagle CAD still has a free tier. It¡¯s limited to 2 signal layers and 12 square inches of PCB area ¡ª both of which are sufficient for most mic circuit designs, in my experience.
The interface is famously inscrutable, but there are many online resources to help decipher the tools.?
Its 3D integration is not great, but likely to improve now that Autodesk has both Eagle and Fusion 360. I¡¯ve seen other CAD apps that output a 3D rendered visualization of the PCB layout. Eagle doesn¡¯t seem to be there yet, or at least, none of the component libraries I use have any 3D models attached. Perhaps that¡¯s still to come.