I don't think it will be that expensive, given we're talking about a set of small OLED panels in the headset, probably a smaller chassis than what we see in the prototype, basically plastic, some Move style sensors built in, lights for tracking.
If Sony wants to add power then they could have an additional GPU (PS4 level of spec) and RAM (maybe 3GBs of GDDR5), running in Cross Fire in a module you connect to PS4, that is if they don't want to downgrade the visuals of games, if they want it to run natively, with no frame drops at 120FPS.
Price wise I don't think the headset and an additional module would come out at more than $200/£150 at launch, but it would be better if Sony could get it down to $149/£99, because adoption rates will be much higher, they can subsidize with fun novel theme park style software, games, experience things.
