At this point its nothing but rumor, because we only have half the hardware in question right now.
I would already make the bold statement that the 360 and the PS3 will be the same on a non HD TV, they will both probably be too graphically superior to notice any difference on an old low res tv. Now when you bring HD into the picture I dont know, its anyones guess.
And the PS3 price point is high, but just the fact of the Blu-Ray player will be a big selling point. Remember now, the 360 is getting an HD-DVD addon USB drive (rumored to cost 200$ and launch when the PS3 does)... that means the 360 is whatever you already invested into it (400$ in most cases) + another 200$ for the HD-DVD drive. I dont know what they intend to do with HD-DVD though, release games on it or use it for a movie playing drive???
But that puts the 360 preimum + supposed 200$ HD-DVD unit right on par with the 599$ 60GB version PS3.