In my view, $70 per light is either a bargain or rip-off depending on how you value your time. I have tried a couple of kits and looked at several others. They are mostly worthless.
The actual process is simple and I relatively easy to so, but it takes time to do it right. Some of the kits only provide a polish that will fill in some of the haze. These work for a while on minor problems, but the real repair requires restoring the original optical finish on the plastic. I proceed as follows:
1 - Tape off all body work so only the surface to be finished is exposed. Use plastic sheets and tape as this will be a wet process.
2 - Start with 400 grit wet or dry sand paper (From an auto parts store) Tear off a piece about 4 inches square.
3 - Dip it in a container of water and start rubbing the foggy light. This will scratch the light and make it even more cloudy than before. Do not be alarmed just continue dipping and rubbing.
4 - After a while (5 minutes or so) wash with clean water and dry.
6 - Look at the surface. if the entire surface has an even finish continue the process, if not go back to step 3 and repeat until you have a uniform finish.
7 - It is important the finish is uniform. If scratches or other defects show up later, you will lose all the work past this point.
8 - When you have a uniform finish, throw away the square of sand paper then carefully wash the entire surface including the plastic surround and your water container. If you leave any grit from this sandpaper it will later scratch the surface and you will get to start over.
9 - Select a square of 800 grit sand paper and repeat the entire process.
10, 11, 12, 13 - Repeat again with 1200, 20,000, and finally 50,000 grit. You are almost finished. Clean up, remove the covering and polish the now perfect light with any good grade of plastic polish. It took me about 1 hour per light and a lot of elbow grease. While I am glad I tried the process and the results are still good 4 years later, the next light that needed repair, I paid $120 for a new light. Your time may be less valuable than mine.
A Side Note: I recently watched folks at Camping World do this task. They use a power sander and a dry process. The results look good and I suspect it took about 30 minutes per light so $70 sounds reasonable to me.