All of the hardware in this thing is stuff you would see in a very high-end phone (CPU, GPU, 3G, GPS, Wifi, OLED screen, etc). Granted, we will not have this until later this year, but even then it will still be very high-end gear. But just like a very high-end phone containing those types of high-end parts, if you try to buy one with no contract, they are almost always over $500, at least, if not $600-700. The only way that I can see Sony getting this under $300 is if they subsidize it for its 3G connection.
If they do that, then sure, $200-300 is possible, just like any other high-end phone hardware. Without that, I just honestly can't see ALL of that hardware being sold for anything less than $400, without Sony taking a huge loss on it. And after working so hard to get the PS3 back to profitability these last couple years, the last thing they want to do (one would hope) is go right back to taking a loss on hardware. Does the general public REALLY want to carry around yet another device to play games and media on, when they already have that with Android/iPhone/etc? Especially if that 2nd device is either very expensive, or requires another monthly charge?
I don't know how to answer to those things, but it will certainly be interesting come E3 to see how Sony does.