HIDs as with anything, you get what you pay for. That's not to say that going out and blowing money on the most expensive kit is what you should do. I know several guys running kits from EBAY that were around $50-$75 and have had no trouble out of them. Biggest thing to look for in my opinion is a ballast that's fully potted. Just about every "slim-line" ballast is and makes a huge difference in the life of the kit due to vibration resistance and protection from moisture. Light output on a projector is usually more focused and will project longer but I've always found it makes field of vision more narrow. As long as you don't exceed a 50w ballast you shouldn't have any problems with running the kit in factory headlights. The smaller the light housing the more focused the heat is going to be so I might stay around 35w on the fogs.