Development of the prototype's firmware to 'feature demo' status will be the bulk of the product development work. The PCB design will be mostly moving the DevBoard's electronics to a new PCB, and adding missing features (e.g. power mgmt, user interface).
It is close to impossible to develop a feature-rich 'demo' video pipeline that isn't nearly a production ready video pipeline, unless you make it using resource-hungry (and maybe expensive) IP blocks.
Odds are that an IP-based pipeline won't fit in the target device that meets your price point, so you will need to throw it all away and then perform a complete lightweight re-implementation - starting from nothing again.