Actually, now that I think about it, can I talk you into spending just $100 more?
If you were, for some reason, limited to only one lens, there are many people on this forum who would argue for the Canon 50mm f1.8. With that lower f-stop, you'll be able to get a more shallow depth of field, and the ability to shoot in lower light. And aren't those two major reasons why everybody is swooping up these cameras?
Me however, in this nifty fifty vs. kit lens debate, I would side on the kit lens. Personally, I just can't imagine doing a shoot without a wide lens. In my book, it's just flat-out a necessity. Especially as an ultra-low-budget filmmaker, your location isn't always ideal; you often have to settle for what's available, not what you want. And in those situations, you might be in cramped quarters, or maybe you want a shot from a particular angle, and the only way to get it is with a wide lens. I wouldn't want to go without it, ever.
Thing is, though, do you really need to limit yourself to one lens? We're talking a measly stinking $100. Even if you're a minimum-wage worker, that's just a couple days' work. So, my vote is for both.