Another possibility to consider is buying the BG-E8 battery grip. You're a filmmaker, and I don't know if filmmakers like those battery/power grips on their DSLRs. Do they fit well with the rigs you use etc?
Well, here's a videographer who's using the 5D power grip with his 5d apparently.
https://www.youtube.com/watch?v=7MpwAOaTO4w
I recently bought a Canon DSLR, and one of the first things I did was to get the power grip. But I wanted the vertical grip with shutter anyway, because I'm into still photography. And I wanted to know I could use common AA batteries if for some reason I found myself with uncharged or dead chargeable batteries.
Looks like the T3i grip sells new at 136 dollars. But you could look around for used ones.