However, if I could have them installed for $600, I wouldn't bother doing it myself. We have a little bit of a cartel behavior with AC installers at least in my area of the US. Even though the job has gotten much easier with mini splits being requested more, they're unwilling to give up the amount they were making per job with Central units.
A fine I presume, if someone figures out. You'd have to get the unit second hand or similar, all stores are required to ensure you've ordered an installation from a certified company when they sell it AFAIK. Last ones I bought, a few years apart, had it all integrated in the web shops. Just selected installation company from a dropdown, fixed price for basic install.