Those extractors look ok, but don't expect huge gains. Exhaust/intake mods are good for helping the car breathe better and can give you gains in areas like throttle response and smoother acceleration throughout the rev range. But don't be mistaken for thinking you're going to notice big power increases.
There is really no such thing as cheap power in the car game. And if it is cheap it will probably cost you more in the long run to replace if/when it breaks. As the saying goes: cheap, fast, reliable - you can choose only two. Cheap and fast, won't be reliable; cheap and reliable, won't be fast; fast and reliable, won't come cheap.