Its alot easier than it sounds ..and don't go blind on the diagram spec r put on if you have a little eletrical know-how you can do it.
The most important thing when looking for an hid kit is the type of bulb.. h4/h3/etc/etc. I put bmw hids on my old 86 rx7.I just had to get different bulbs but I used the ballast and igniter from the bmw..

If you look at the diagram..the major things you need to ensure you connect is the lead and ground...fairly dummy proof.

Now as for cost the cheapest I've seen is 300 at a junk yard.
The owners don't like to let go that kind of stuff easily.
Your best bet is to find a set that "fell off the truck".....
If you know what I mean......

ps- I do NOT encourage stealing....IT IS WRONG!!!!!