How can you say that with such certainty? I moved from Washington, DC to the Bay Area last fall, and my costs were significantly higher than $1000. Even if I cut all the corners, a hypothetical move to Boston would still cost me thousands of dollars.

If I was doing YC for a summer, I wouldn't need to move. I could just fly there with a couple of suitcases and a laptop, but I'd need some way to cover my existing apartment rent. That's a pretty significant expense over 3 months. And I suspect YC is not looking for companies who see the experience just "doing YC for a summer."