Depends if you get a clone or like a legit one. A legit one is like better quality material, and a clone is kinda like a knockoff. So the prices could vary from like $40-$300. The only downside is that you usually have to buy all the components separately, but the difference in the actually smoke is a huge difference from a regular vape.
http://www.fasttech.com/category/3027/mods-mechanical/ This is a website where you can buy the components and you put them together. And the difference between a mechanical and like another vape is that in the mechanical, the battery heats up coils, burns the cotton with the liquid, and you get the smoke.