Folland Midge
Yes, it was the forerunner of the Gnat, but surely this ticks a few boxes: light, manoeuverable, low-cost (potentially): http://www.britishpathe.com/video/worlds-lightest-jet-fighter
Yes, it was the forerunner of the Gnat, but surely this ticks a few boxes: light, manoeuverable, low-cost (potentially): http://www.britishpathe.com/video/worlds-lightest-jet-fighter