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.
I'm sure you can't imagine, I haven't described the film project, or my equipment, the story, my vision for the film, or anything else. I wouldn't expect you to understand why I want to control it with the iPhone, just that I do and I know it's possible. It works for my film. This is my first robot, not my first film. That's why I came to this forum— to ask about the robot, not filmmaking. I know exactly how I want it to look, and how I want it to behave. I started this thread asking if the parts I had thought would be adequate would actually be enough to get the robot to take commands via the iPhone as a controller. Basically, I wanted a list of parts that would work for what I described. If it's above my budget, I'll deal with that somehow, but I really just wanted to know what I was getting myself into with the robot alone. I feel like people are getting way too caught up in the fact that it's for a film and questioning why. It's a prop, not a piece of equipment. I need it to do certain things (specifically, move on command) and look a specific way and be controlled easily, and not via laptop. That's all.
I thought building a robot that could move and be controlled remotely would be really basic. It seems I was very wrong.
If you only have $100, you may need to consider possibly an RC rock crawler for your bot platform.
That's a great suggestion, and really, I want the bot to be controlled like an rc car, but I've already been down this road. This was, actually, the very first thing I considered, but an r/c car chassis looks like an r/c car. It is important that the robot actually looks like a ROBOT, not like a car. That's why I chose this platform: http://www.amazon.com/gp/product/B007JZ2ICW/ref=s9_wish_gw_d2_g236_ir02?ie=UTF8&colid=2COHY7RKP0O04&coliid=I243EGR0M4DTBQ&pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-2&pf_rd_r=05EMV2QDXZ2RFQWNN6WN&pf_rd_t=101&pf_rd_p=1389517282&pf_rd_i=507846
That has the look I need. If I could find a small replica of a Mars rover that was r/c and didn't look like a toddler's toy, that would be awesome too.
Now, if there's a way to get all the controls from the car, and put it in that platform, so it moves and looks like a robot but has controls like the car, that would solve my problem. Is that possible? If so, I'll gut a car and put that in the platform I like.