Hey, I’d estimate around 5–7 hours for the first version, so US$100–$140 at $20/hour. That includes testing it in your scene and tuning the movement and camera feel, with the code set up so the later mechanics can be added without reworking the controller.
I don’t currently have a public 3D first-person Godot sample to share. Desktop Reptiles is the public Godot project I have available.
If that range works for you, send over the project and the exact Godot 4 version. I’ll take a look at the setup before confirming the quote.