PlayStation and PS2 both launched at $299. Both turned out to be among the most successful consoles ever seen, combining the appeal of state-of-the-art technology with a just-about-affordable-if-you-really-want-it price point. By comparison, PS3 launched at $599 and everyone laughed. It was necessary due to the expensive development of Cell, but PS4 uses PC components, making it more likely to fall back in line.
While a sub $300/£300 price point for PS4 would be killer, we don't know if that's possible. What we do know is that Sony will aim lower, possibly coming in around $400. And even if all that wonderful techno-jiggery costs more than that to produce, it’s imperative Sony learns from Nintendo (and Vita’s) mistakes and takes a hit on console profits in exchange for a large user-base.