Air-to-Air heat pumps can be quite affordable. Or even cheap if you find no name deals. There is install, but even that is not really that significant. This is at least in Nordics.
The install itself isn't that hard they come pre-charged with refrigerant. I have installed a few of the air-to air myself and had no issues. All you need is a vacuum pump and proper refrigerant manifold or adapters. Vacuum out the lines for at least an hour to draw out all the air and moisture, close valve and let sit for an hour, if the gauge shows no leak, open the heat pump zone valves and you're in business.
A friend did it and had all the refrigerant leak out after a year but he realized the flared end that came from factory was malformed so he cut and re-flared the end, vacuumed out the system, left it overnight, saw no leak, and had an AC tech do the charge. Was solid after that. A from zero charge requires some knowledge of the systems capacity and a scale to weigh the charge so he hired someone to do it.
Example: https://www.highseer.com/products/pioneer-kwik-e-vac
I think I spent $200 in parts on Amazon and have done 4 heat pumps now. It's a vacuum pump, a scale, and a digital manifold/guage. Punch the numbers for subcool/superheat into a calculator and use the temp probes on the lines where they connect to the condenser and you can even skip the scale.
In the US, you can get your EPA 508 cert online in a couple hours and buy the refrigerant online. (You need the cert to be legal, but it’s not really checked just to buy.) Tightly regulated is not true in practice. You could buy some in 3 minutes online and have it Monday.
In France, access to the gas technically requires a certification that is not available to regular people. You need to be professional and bow to the bureaucracy.
I know somebody who was required to pay the full installation price for a heat pump he installed himself because there was no professional that was willing to charge and launch the installation for the small fee it should require.
This is the hypocrisy and value-destroying behavior of EU collectivist governments. They tout ecological solutions, but you need to pay far more than is reasonable for those modern solutions. Predictably, people chose things that are worse but cheaper, like wood-burning stoves or pellet stoves.
Those things are made artificially expensive for no good reason, and that's because they get built overseas mostly, and this happened because of regulations in the first place. Then they wonder why the EU is losing ground economically…
From what I understand, self-install should be fine up to a 12m run, but if you let too much gas leak, you may have issues because of low pressure.
At least now you can buy them for relatively cheap. Mine required a swap of the control board on the inside unit, and it was ridiculously expensive (almost as much as buying a new unit). I am not sure why it fried, but probably bad solder from old age (it's about 15 years old at this point).
It's an excellent technology, but the surrounding business feels extremely shady.
But then neighbours start complaining about the look of the outdoor units and causing hassle with court orders etc. Really if they want people to move they should make it easy and cheap, so invalidate cosmetic complaints automatically.