If you can get the VIN of the Mirage you are looking at, we can find the Monroney window sticker and see exactly how it is configured. Or, post a link to your dealer's page for that Mirage.
If you really want to get a Mirage, you can save a lot on the purchase, justifying the cost of getting there.
Be certain that this little car will suit your needs before going further. Let me ask you a question - what was the smallest car you drove? Some folks cannot abide by such a modestly powered car, but that a big reason why the Mirage gets such good fuel economy, and that is the whole point of this car.
While I like their music, I disagree with their lyrics. That's Slayer.
When you compare the cost of buying an amp & subwoofer, the Mirage RF kit is a bit pricey, but not much. When you consider it has plug & play wiring and mounting hardware, and is custom tuned for the Mirage, I think it's a fair deal.
But I'll suggest that the audio system should not be the main reason for buying a Mirage in the first place.