It costs almost nothing except a small piece of aluminium foil. Before I have this reflector, the maximum aperture I can have is f/11, any smaller aperture will cause insufficient light (or any smaller aperture with slower shutter speed will cause image blur). Now I probably can stop down until f/16 or even f/22 to achieve more DOF while maintaining my shutter speed.
However its raining when I completed this, I will try the effect when I have a chance.
UPDATE: Here are pics taken by this set-up on f/16. I finally can stop down to f/16 or more while retaining 1/200s shutter speed.
As you can see, the lighting is better than last time, however, the major problem is the reflection, it is a bit too strong where some of the details are blown out. I still need to fine tune my set-up.