Initial price is critical because initial reviews and overall reputation will be based on that. Nexus 7 shows that pricing cheaper doesn't harm the product perception if it is clearly a good product.
The other issue if pricing is deliberately set with particular reference to the iPad is that it might need readjust everything when the next Apple product arrives.
The main thing they need to do is show that it a really great product. If it is better than the iPad at three things but there is on dodgy aspect that is what everyone will hear about.
Who is the target market for the Surface? Those who would otherwise get a Netbox/laptop? Existing iPad owners? Current Windows users with no tablets? Mainly business?
I think if they want to hit the non tablet owning consumer they need to offer better product than the Nexus 7 at pricing just a bit higher. I don't think that they can match price with the iPad for that market unless people are treating it as PC replacement (which is dangerous ground for Microsoft but may be the correct self disruption move in the innovator's dilemma.