You can also make one yourself on the cheap if you'd like.
a basic parts list:
pvc pipe or dowels.
scrap wood blocks (something to serve as a standoff)
wire (large enough to handle the current you'll be drawing)
dryer vent hose (the collapsible white vinyl stuff, this will get worn out, so get the cheap stuff and just plan to replace it once in awhile)
a 55 gallon drum
a 4 wheel dolly, or some sort of wheeled base (this thing is damn heavy when full of water)
some sort of heating element.
a squirrel cage or other such blower, doesn't need to be a huge one.
a milk crate or basket (you can line it with screen door mesh if the holes are big, you want it to hold golf ball sized chunks of dry ice)
silicone rtv or epoxy, something you can use to waterproof and insulate. with the constant temperature changes, I recommend rtv or something that will stay flexible.
get a 55 gallon plastic drum from a salvage yard (I would recommend an old coke syrup barrel or the like, as they're less likely to be full of nasty chemicals). you want this barrel to have a top.
from that same scrap yard you want to find a squirrel cage blower or the like, and some sort of basket (a milk crate works well). Try to find a dolly or some sort of wheeled base, as once this is full it's really damn heavy. also look for an old electric water heater, you don't need much out of this, just coil. You can also get other elements, depending on how quickly you want your water to reheat. you can use elements from hot tubs as well, and perhaps even stove eyes or oven elements.
once you've got all the parts, you can start putting it together. cut a hole the size of the basket in the top, and mount the element safely inside the tank and wire it up, test to make sure you're not going to electrocute yourself. once it's safe, use some scrap blocks of wood to make a standoff so that if the basket crashes into the barrel it won't hit the element.
to build the basket assembly. take your milk crate or what have you and attach a length of pvc pipe to two opposite sides of it. put this assembly in the barrel, and cut holes to let the pipes come through the top so that the pipes can be used to raise and lower the basket into and out of the water. I also build a "handle" at this time, by taking two pvc elbows and a short piece of pipe to connect the two pipes coming out the top of the barrel.
once this is done, pull the basket to the top. mark and drill a hole in each of the pipes where they meet the top of the drum. you can put nails through the holes to hold the basket up and out of the water.
at this time, you want to cut a hole on the side of the barrel for the dryer vent hose. make it as high as you want (the higher on the side, the more water, and the more fog), I would go an inch down from the top and make the hole there. cut another hole in the top of the barrel and attach the blower to it, so that it blows down into the barrel and exhausts out the hole in the side.
then take another scrap of wood or plastic and make a hatch for the basket hole. you want this to cover and be as airtight as possible. smoke will come out of this anyway, so you don't have to get really anal about it.
anyway, once this is put together, fill it and let it heat up. you want to watch to see how hot the water gets, just under boiling is about as hot as you want to go, depending on your materials and their temperature ranges, you can go hotter, but I don't know what would happen.
ok, so this thing will use a ton of dry ice, I recommend 50-75 lbs of dry ice.
put on a pair of welding gauntlets to work with the dry ice so you don't burn your hands. lay it out on a towel and break it up with an ice pick to the size of golf balls, save all the little pieces and such, as they will make smoke too. I usually dump the dry ice into a 5 gallon bucket, as it makes it easier to load the machine, but you can just dump it in the basket from the towel. however, you don't want to add any dry ice until you're ready to make smoke, as some little pieces will drop into the water and start going.
anyway, to smoke, dump the ice into the basket. close and latch the lid and then pull the nails out of the pvc pipe to let the basket submerge. then just point the hose where you want and have fun.
"TO DO IS TO BE" - Nietzsche
"TO BE IS TO DO" - Kant
"DO BE DO BE DO" - Sinatra