Why Verge3D if we have Three.js?
It's not a secret that Verge3D is based on the cool and really popular WebGL framework called Three.js. Three.js is open-source, so you can download and use it completely free of charge. So what makes Verge3D worth the money?
Way better Blender, 3ds Max, or Maya integration
Older versions of Three.js included exporters for these modelling suits, but it's not the case anymore. Instead, you should rely on third-party exporters to the glTF 2.0 format and GLTFLoader plugin which should be attached to your application by hand (it's not part of the Three.js core library). Basically, to make something you need to constrain your scene features to fit into glTF 2.0 standard and be a JavaScript coder to be able to render something with Three.js.
With Verge3D it's a completely different story. The framework was designed to be an artist-friendly tool. You just need to have some Blender, 3ds Max, or Maya skills to make any kind of 3D web content with Verge3D. Moreover it supports features of these modelling suites (cameras, lights, shadows, constraints, animation, etc) natively and strive to make Verge3D renderings look exactly the same.