In the software world a prototype is eons away from a product that would be considered "beta". Website prototypes typically have one or two functions that actually work; most everything else is just the front facade to represent what it will eventually do. The main objective with a prototype is to demonstrate the proof of concept.
A product in "beta" is a completed product that has undergone all unit testing and is ready to be stress tested by a subset of users to find bugs that don't show up in unit testing.
So... which one do you really want-- a prototype, or a completed product? Assuming prototype, what is your budget for getting it created? Is your angel investor willing to invest $500 into its development? That much should get you a prototype with enough working parts (or simulated working parts) to give his partners a solid idea of what the completed website will be.