If you absolutely cannot pay anything, use these alternatives that work with SketchUp 2018:
If you use multiple machines, you can select V-Ray Swarm during advanced installation to enable distributed rendering. 3. Optimizing Your Workflow Vray 3.6 Sketchup 2018 Patch
A centralized hub to manage V-Ray assets like materials, lights, and render settings without leaving the SketchUp environment. If you absolutely cannot pay anything, use these
To run V-Ray 3.6 smoothly on SketchUp 2018, your system should meet these standards: V-Ray 3.6 Released for SketchUp - Engineering.com If you absolutely cannot pay anything
The rendering world has changed. V-Ray 3.6 is now obsolete. It does not support:
Do not risk your portfolio, your client data, or your personal finances.