Best software for reliably converting between video formats

I often have to convert my client’s video files from mp4 and other formats to wmv. Right now I am doing that rather expensively by using Media Encoder for $29.99 a month. I’m guessing there are software products out there that can do this reliably in a way that will be much cheaper for me in the long run. If so, could someone please suggest some? I need a product whose output I can rely on, that works with all major formats, and which preferably gives me the ability to tweak different options such as number of passes and video screen size. Thanks much for any ideas.