Argus As 014
The Argus As 014 was a pulse jet engine used on the German V-1 flying bomber of World War II. This was meant to be a simple model that would have been easy to make a lot of for not very much money. The engine was made from a sheet of steel that was rolled into a tube. A shutter was placed at one of the ends of the tube, along with a fuel valve and an igniter (something that lights things on fire).
It was thought that this could become a good power source for some last ditch German fighters during the last few days of World War II.