+1. Yep. Ignore the haters or people who think its expensive. $6k is not that much and you'll probably spend over 100 hours on this (and I'm not even including server costs/setup). All software project planning is guessing and kind of worthless, no matter how simple the app seems from the start; there are hidden costs and time sinks you will never know about beforehand (like this thread of holier than thous). You should get a decent pay out of this especially for the time and risk exposure. Everybody's a naysayer and wishes they could do it too. Let them. Talk is cheap, and so are cheap services and people who can say "I can do it cheaper." Just forge ahead despite the criticism.
I agree with the haters gonna hate comment. I disagree about the second part - investors aren't supposed to pay him salary so that he can work on his own project during his free time, especially when investors aren't getting back anything other than thank you's. He will have his salary paid once the project is finished (if it's any good). Of course it would be a bit different if the project would require many months of full-time commitment.
Another way to look at it is that an investor could pay him monthly salary + expenses, but then the end results (and profits generated) would belong to the investor.