From what I've read the volcano is AMAZING, best thing out there. Basically its got a computer that figures all the variables on the inside, and when things are just right, it blows into that bag, making the thc smoke somewhat portable. Although after about 10 min the thc recondenses and you lose out on a sweet high. I've seen them on ebay for 540. In my opinion its not worth it.
If I can get some money and time to work on it together I'm going to try to build a diy volcano. You can buy their bags online for cheap. I'm going to build the base with some simple electronics, including a thermometer, and probobly a fire detector, but I'm not sure on that yet. Basically use the thermometer and experimentation to find the IDEAL temp to heat at (keep in mind might not be the exact boiling point of thc). Then keep heating at that temp until the fire detector sense lack of oxygen. Instead of ringing a bell, it will activate the fan which will blow all the thc smoke into the bag.
The vapor brothers unit, is much simpler a design, and supposedly can work almost as well (minus the bag, and the computer). It runs about 120 on ebay, and has nothing but good reviews. It's the vaporizer I'm looking to buy.