That price sounds pretty normal considering the offering... phones are expensive these days and this isn't a low end device, nor a low end target market (corporate office workers).
It's substantially lower in price, at $229.99
I'm no phone expert, but the premium for the keyboard plus a slightly larger battery seems off to me.
I don't know what exactly BlackBerry has committed to in terms of security updates, but if buy this phone and I get very timely security updates for the next 2+ years, that has a lot of value to me.