Windows 8 pricing - how much would you pay?

Unlike most in this forum, I'm not a died in the wool Redmond supporter. I've only bought Windows computers, but that's because they're cheaper. I have an Android phone, and I own a PS3. That said, I've been hugely impressed with the direction Microsoft has taken in recent years, and I absolutely love Windows 7. I'm also rooting for Windows Phone to make a dent in the market (competition helps everyone), and the idea of having Metro on my computer is really appealing. That said, I'm certainly not willing to pay +£100 for what will largely amount to a skin. What do you guys think is a fair price for Windows 8? OS X Lion is £20.99, and I would definitely pay that for Windows 8.

Doorknob question: I'm on middling hardware (i5, 3GB) - is Windows 8 likely to impact performance?