You need $50k to live for a year? Where are you living?
People often forget about how many of their costs don't exist if they're not earning income: Obviously you don't have to pay income taxes any more, but also the cost of commuting disappears, and the cost of food might drop dramatically (depending on where you would eat lunch if you had a paying job).
I'd say that YC's $5k + $5k/person funding formula is about right -- $5k is likely to cover startup costs for a company (at least, for the sort of companies YC funds), and $5k should be more than enough to live off of for 3 months.
But not if you have a mortgage, student loans, a car loan, maybe some credit card debt, etc.
And rounds of funding can take months to close, so it is more like $5K for 7 months, not 3.
I seriously doubt pg actually expects people to do YCombinator with $0 saved up and tons of debt and live on 5k for 3 months. Or worse, with an illness or surgery that needs to be done. Get all that out of the way, pay off your loans and credit card debt, and save up some money by working corporate. Plus you'll have experience, good references, friends, and maybe good contacts from working at a company.
I used to think I was old when I turned 21 and 22, but if you're 25 or 30 when you start a startup, that's fine! But before you work at corporate, make sure you do your own startup with customers and everything in college so when you're hired, you're respected and management wants to hear what you're saying, rather than HR placing you in a "trainee" program like two high school acquintances my age will be at the same company for the next two years. That gives you credibility from your coworkers, experience leading your own project from your startups, and a degree you've been able to pay for. Maybe you could even get a Master's degree in Business or Computer Science that the company will pay for while you work.
This means you won't be a "millionnaire by the time you're age 25" like everybody our age who's heard of Bill Gates during the late 90's has wished for, but getting out of debt by the time you're in mid-twenties is the new "being a millionnaire", with the cost of everything these days.
Is that what the kids are aiming for these days? Back when I was in high school the goal was "millionaire by the time you're age 30". Oh how times change.
That is the right question to ask. People will made due -- not all the money needs to come from YC. Personal savings, credit cards, friends & family (both money and spare bedrooms), etc. make up the difference.
An underrated startup technique :)
Sure -- I'm a bit skeptical about the YC model of providing funding for only 3 months, too. My point was more that for someone accustomed to an undergrad or grad budget (which is probably most people here), $20k for a year is far more reasonable than $50k.
Most people I know and startups I have been involved in start off with cash from friends and family. One of the most difficult leaps you take is quitting a paying job and taking a small sum of money and trying things out. VCs definitely want to take an idea/product and scale it like you mentioned.
The one thing I would suggest is do you need 500k to start a startup? I would suggest the number is closer to 1/10th of that to survive for a year, at least as an Internet startup.
EDIT: To clarify, I meant 1/10th of that to start a company for a year, not to personally survive for a year. There are many necessary costs for a company that shouldn't total more than about that 50k mark, lets call it "servers and shit" costs. I was completely excluding living expenses!