Jason Striegel, editor of Hack A Day came up with this low-tech version of an espresso machine using PVC pipe and a caulk gun. In theory, if the water is the right temperature and you manage to create the right pressure with the plunger, you get an espresso.
From the pictures, the result is not pretty and probably doesn’t come anywhere near a real shot of espresso, I can’t see any crema in there. You are probably better off getting a cheap stove-top mocha maker, but Jason gets and A for effort.