Hi! If you are targeting VR and realistic environments, I would pretty much stick to Unreal Engine, not Unity3D, but you need to check that you are OK with their license models. Secondly before any kind of bid estimation, I need to know the length of the game, gameplay complexity and e.t.c Do you plan on assembling environment by yourself? In the end, they are still going to be full 3D textured models, correct?
Regards,
Konstantin.