Why?Are you going to film the iPhone? Will you be using your iPhone to do the recording and make the coffee too? Or is this a totally arbitrary requirement that you're introducing because you think it would be fun? There's nothing wrong with doing things for the fun of it, but don't kid yourself that this requirement is anything to do with film making.Your main decisions should be what's it going to look like (the shell) and how is it going to behave (the drive mechanism). Unless your control system is going to be part of the resulting film, anything else is irrelevant. I can't imagine why you'd be looking for anything other than a conventional radio control system and the chassis from a model bought off-the-shelf from the requirements you've described so far.
If you only have $100, you may need to consider possibly an RC rock crawler for your bot platform.