A good way to save some money is by not replacing faded and scratched rear light lenses and turn signal lenses with pricey OEM ones.
The lenses alone might save you just a little money. New OEM rear light lenses + front turn signal lenses will cost you around $80 total, but the rear reflectors will be a good thing to consider giving a second life, since they will be around $120 for a OEM replacement.
First I clean the lenses with regular soap on both sides with a nailbrush, or a smaller brush for the hard to reach spots.
Most of the time the dull appearance of the plastic is just a surface issue. Therefore the solution is to polish the plastic with a mild rubbing compound. Try to start with a soft one, like a chrome polish, or a mild paint polish paste. Because the plastic is fragile, the results will show quickly. Do not use an electric polish device (dremel etc), it will produce to much heat and melt the plastic!!
After that I clean brush the lenses with some water.
In case of the reflectors, the black plastic base might be faded to a grayish color. First polish this as well, so the surface becomes smooth and the scratches less noticeable. Then I use a car-product like “Black chrome” or “bumper black”, that is made for dying automotive plastics to a fresh black color. Just apply some on a soft cloth and gently rub it onto the base. Let it dry for a few minutes, so it penetrates the plastic, when its dry, Rub the surface with a soft cloth until it starts to shine with a fresh black finish.
At least, that’s how I do it.