I would keep an eye on MonoGame. It's open-source for a all desktop and mobile platforms and they have recently announced a paid PS4 support is in the works. I

I would keep an eye on MonoGame. It's open-source for a all desktop and mobile platforms and they have recently announced a paid PS4 support is in the works. I think it's likely to be much cheaper than Unity3d. Of course the tooling is not there yet...