Should I buy a 2004 Ford Mustang with 184,xxx miles for $2,500?

Automatic transmission runs good everything works

That's pretty much in line with what Kelley Blue Book says. If it sounds good, rides smooth, gets up to 60 mph okay, tires have some tread on them, it should be okay.

As long as you expect to only get 2-3 years out of it, sure. It is as good as you will get for the price.

It's the hidden problems you have to worry about. Get a professional mechanic to check it out before you buy it. Otherwise you risk buying a $2500 car that needs $5000 worth of repairs.