Do you need to shoot a scene that needs a smoking engine? How about one with decayed zombie hands reaching up out of their fog-laden graves to grab the ankles of unsuspecting victims?
Then you're going to need some smoke -- or fog -- or whatever you usually call that heavy white vapor that always makes scenes look so good. We've talked about the benefits of using smoke on-set before, how it's a great cinematographic tool that can add depth to your shots, diffuse light, or simply create a stylistic atmosphere.
However, if you're looking for cheap, DIY solutions for smoke effects like the ones named above, then you'll want to check out this video by Film Riot. In it, they show you how to make super dense, low-hanging fog by combining a smoke machine, a styrofoam cooler, PVC pipe, and a block of dry ice.
I love this set up so much, because not only am I a lazy fool, I'm also a lover of both MacGyver and dry ice. We posted a video back in May of a DIY solution to cooling fog so that it thickens and hangs low on the ground, but it was admittedly a little too labor-intensive for my taste. It also used ice cubes instead of dry ice, which, I'd assume, would melt quickly under the heat of all of the lighting equipment -- then you'd have to constantly be having to replenish the cubes in order to cool the fog and it'd just be a huge, wet, stupid mess.
The only issue I can see people having is being able to procure a smoke machine. I know that I could go rent or purchase one at any number of stores in my area, but I also know that not everyone can. If that's you, dry ice can give you at least some of the effect you're looking for, though it's by no means a substitute. Also, it's messier and more dangerous and would require a lot of receptacles. If you do have access to smoke machines but they're a little outside of your budget (a good one costs about $150), renting one is a good option, too -- though after you see what it can do for your shots you'll want to use it all the time. You'd eventually end up spending the same amount of money (or more) on rental fees anyway.
Like we've said before, these things can do wonders for your shots and is certainly an area of cinematography that is well worth your time to experiment with (and become the lord of) it.