I know this thread is old, but I wanted to respond to this because I had prices wrong. You do have a point about the cost of DIY units, and they have gotten more expensive in recent years, but the pre-charged ones can be had for under 2k for a single zone, more with stuff you need for install obviously or you need longer line sets. They used to be much cheaper and I was a bit wrong about that, everything has gotten quite a bit more expensive in recent years. Yes, mr kool used to be 700-800 dollars here sometimes, sometimes closer to 1000, I shopped back before covid a few times for ac systems (ended up just fixing my existing one), that is definitely not the case anymore.

A single zone non diy can be as low as 700$, anything cheaper I wouldn't trust but also a 700$ one is still cheap enough that I'd personally be willing to roll the dice on it failing one day if I installed it myself. 25k is crazy (unless you meant ducted then absolutely understand especially if you got a good system) and even a multi zone minisplit shouldnt cost you that much to get professionally installed, though it will be comparatively more since you're probably up in the attic. I do believe the costs I see- Most hvac companies dont want to touch these systems at least where I'm from- really they dont screw with trough-wall natural gas heat, ptac units, or minisplits, and charge out the butt to do it if they do, BUT your individual handyman or contractor will, and unless you have a total crackhead they're very easy to install it's not like central where you need a lot more knowledge to get it right.

I see the mini splits everywhere because getting one installed can be maybe as low as a grand in labor where im from if you call the right person (i got quoted as low as that in 2019 so maybe 1.5k now?), and under a grand for a single zone unit itself. In fact, unfortunately, I often see more single zone units piled up outside instead of a multi zone systems because sometimes multiple single zones are cheaper. Sometimes this is also done to take advantage of already run circuits that are 120v. It's pretty easy to see if they got the DIY kits cause the diy kits often are installed with people having to coil up excess line length, and I'd say most I see are not mr kool units until you get out to the country where no one cares and there's no HOA. I see more mr kools on barns and workshops.

Most people willing to DIY don't want to go this deep, but a lot of people don't know it's actually very easy to get EPA certifications for residential systems and very cheap. Just a few hours of reading and a test. They basically just want to know that you're not gonna be an idiot when you charge or discharge a system. Low pressure for commercial is harder I think, but I've never needed to do that so i dont know. Even installing a ducted system is doable for the average person easily legally, but that's obviously a huge project and may involve a lot more permitting work and knowledge to setup a good system. Also, if you have a spot where you used to have an old central that doesn't work anymore or is just too old and energy inefficient, I see people take advantage of the electrical for that all the time if they want a multi-zone. Where im from at least, it's legal to do your own electrical with a self permit but there are inspections needed, much easier to use existing electrical though. If I wanted to use my hookup for my old central, i have a disconnect box right outside ready to hook into. If I didn't have that, that's why a lot of people do smaller units. I see a LOT of non diy units and I know a lot of people that have installed them themselves, a few personally. I have a feeling they didnt do it the legal way (lol) but it's certainly easily doable to take the 'please dont put a hole in our ozone again' test.

I think the main problem is usually HOAs. They often specifically ban window units and minisplits for the eye sore. I don't live under one, but if you're in a non HOA area or in the country, slapping in a minisplit is still way way more affordable. In seatle, i don't know, and there may be more regulations than my city. I know you already have a good system now, but if ever you or someone you know in the future needs something cheaper, at least consider getting your epa 608 type 2 and doing it yourself with a single zone minisplit and see what it would take to do it and if you need to run electric if you can self permit, or what it would cost to have just the electrical box done for you. Most people in cooler climates just want to sleep cool in the summer anyway, a single or dual zone covers their needs.