For reasons you won't yet comprhend, for video you will need:
A zoom with a fast constant max aperture. That means an f2.8 zoom.
You will need a zoom with a filter thread that doesn't rotate.
You will need a zoom with a nice tactile long throw focus ring.
Such a lens will be really good for your photography, but will really really help your video.
You won't be using AF if you are doing video seriously. People may take issue with this, but they are wrong. AF cannot pinpoint what you want in focus (that is the subjects eye) and cannot track fast enough.
So really forget AF.
You have $500 and a short telephoto.
I would therefore suggest a sigma 18-50 f2.8 EX DC Macro or the same but with OS (not the f2.8-4 version or anything else that sounds similar) can be found used with lots of change, you may be lucky and find a non-OS verison new, and certainly this is the best bang per buck.
18-50 is also a good walkaround lens, decent wide angle, and ok tele. Would be a good interview and GV lens (thinking video) Also has good close focus, it isn't a true macro, but for practical purposes, unless you work in a lab, you wouldn't need a seperate macro lens with this.
I have one and so can recommend it.