It would help if you posted a screenshot of the thing you're hoping to make. The programs you mention are for reliefs and sign work, not so much for full 3D mechanical parts. But depending on the part configuration, they might work to some extent. If your new router is coming from China, the software is probably pirated, so Mach3 will be in demo mode which means it will stop working (if it works at all) after 500 lines of code. That's not a lot for a 3D part. But you can buy a license for Mach3 for $150 and get over that hurdle.
What "light material" are you planning to make this mold out of? What are you going to cast into it?