Hello Charlie,
I'm very impressed with your project. I'm Barbara from IQRIA team. At the moment, I'm a manager in IT, but 2 years ago I worked on FilmStudio, and I had 30 transcribers, who actually write those lines from live. We used FileMaker as a DB for characters/lines/each episode.
As I understand, your project relates for Scenario/translation, right? Or do you need it for editors?
Anyway, it's totally possible for my team, and one more suggestion - for such functionality it's much better to use ExtJS, as it's more useful and comfortable.
About estimate - need a bit more details, I need to understand your goal, to provide you with reasonable estimate.
Let's discuss it here or skype.
Talk soon,
Barbara