It sounds as though your right on the money with a vacuum leak causing your high idle condition and possibly the rough idle.
I just had your identical car in the shop with the same types of problems and found that the brake booster had failed internally and was causing the problem.
Thats not to say that a fuel injector, wiring or computer couldn't be the cause of your problem.
The first thing that I would do is pinch off the vacuum hoses that are coming off of the intake and restart the engine.
If the idle speed settles down, you know that it is indeed a vacuum leak and can then start to trace down the source...
If you are still having a high idle problem, we will need to go deeper...
As far as the last part of your question, the diagnostics should be fairly simple for the right mechanic. We are able to plug in our scan tools and watch the engine control computer and the commands that are given to help determine the source of the malfunction.
Please let me know what you find when you pinch off the vacuum hoses and we'll take it from there.
Without looking at the computer with a scanner I don't want to tell you to throw parts at it. As you already know, it costs way to much.
I'm glad that we atleast now have a reasonable idle speed. You may just need a good run to clean all of the carbon out of the engine that was caused by the high uncontrollable idle speed..
If your rough idle continues, it may be worth having a shop take a look with a scanner to verify all of the computer perimeters...
Please let me know how she does.,.,Thanks, Josh