in bay area, install costs for $2k unit are $6k-$8k (took multiple quotes. 3 years ago). very simple install in garage through the wall. "hardest" part was adding 240v disconnect (electrician did it for $300 or so).
You don’t get the “full warranty” when you DIY hvac installs. You also need to call a licensed hvac tech to charge your system if it doesn’t come precharged. Mini splits are easy and I would 1000% DIY. Big, attic mount blower units I would leave to the pros for so many reasons. That said my cousin installed a 21 SEER unit for $5k. I was quoted $35k for the same system (:
I haven't personally had need to do it (yet), but I know multiple people who got the EPA certification to be able to service their own equipment. It can be obtained by taking an online test.
given installation price vs system price, it's possible to trash old one and buy a new few times for a price of professional install.
mrcool also has ducted units that comes with precharged/vacuumed lines. very tempting as one of my hvacs lives on extended timeline and quote for a new one was $25k 2 years ago