100 bucks is cheap for hids, the problem is that plug and play kits aren't the greatest. They break, are not water proof at all, blind people on the roads and have pretty bad glare. The "right" way to do is to retrofit hids from another car in to your headlights, its alot more expensive but the end result is much better.

While saying that, i still have seen some people pull of plug n play kits nicely when they can angle it right and use a glare guard.