I built an instant pinhole camera out of a Polaroid Colorpack ($4 at Goodwill - a thrift store chain in the US). I just cut the entire front of the camera away with a hacksaw (much to my wife's dismay - she collects Polaroid cameras). Then I built the front up with card stock and mounted a pinhole made out of aluminum foil. You might need to use wood if you're going to mount a lens. I don't know how common these cameras are in Europe, however if you can find one it should work well enough. They're cheap and plentiful here in the States.