Skylight filters are cheap, freely available and come in various filter thread sizes. You will have little trouble obtaining one but you must ensure the correct size to fit your lens. Everyone can afford one and there will be a filter to fit every lens (or almost).
The primary function of a skylight filter is to cut down excessive UV rays which, in turn, make scenes in the distance appear to have a blue haze. The filter effectively reduces the haze and blue colour cast. Pictures of hills and mountains in the distance look clearer.
The secondary function, and why you should have one on each lens, is that of protection. Like a lens cap, the skylight filter fits over the front of the lens and helps to prevent the ingress of dirt and dust. It also protects the lens from the effects of oily and greasy fingers, stick hands and from accidental knocks. It is much cheaper to replace a skylight than it is to replace a damaged lens.