I had a MAC kit (intake plenum and filter) on my 2000 model.
I thik it was about $140.
I never really noticed any change in performance or mpg. Maybe a little diff at real high rpm, but if there was any, it wasn't much.
I liked the filter; being able to wash, dry, re-oil, and re-use.
Some don't like them and think they don't do a good job.
I'm not one who believes that.
I bought a K&N oiled media filter for my 2005 and it too is doing a fine job - at least at 117,000 miles it seems to be.
I went ahead and ordered the AirAid. It's in, but I'm a little hesitant to put it in. If I do install it, and end up getting a check-engine light, will reinstalling the stock unit clear the light, or could it do permanent damage? I was told that with a new intake, more air is given to the engine (duh), and causes the air/fuel ratio to become unstable, and the engine could fail. Not something I want to go through.