$400 doesn't seem like a bad deal. Considering the competition (Facebook's Occulous Rift and Valve's Vive) are priced at $600 and $800 respectively, the price for the PS version seems to be the best to get if one was in the market for such a thing. And clearly developers will have access to produce content geared towards such headsets in order to boost attractiveness of the product. Not to mention it would most likely be compatible with Steam/PC games too. (Negating the need to buy Valve or Facebook's version).
And as technology progresses, the cost of production drops, and so will the price tag of the VR headsets. While I won't be running out to get one now (as there aren't any games I own/will own in the near future that will utilize such technology), if the price ever drops a bit lower I would consider buying.
I got to demo the Occulous Rift at a neuroscience conference last year, and I was pretty neat. Wearing it definitely feels like you are within your fantasy world. The particular demo I got to experience was walking across a plank, then stepping off of it. You definitely feel like you're falling at that point.