In Germany, there are lots of people who plan and program the KNX system themselves. The actual wiring is carried out by a professional but the commissioning etc can be done by anybody. KNX requires a specific software (ETS).
As KNX is a global standard this procedure becomes more and more implemented. We have published an ebook about how to get started with KNX, ETS 5 and ETS Inside (cheaper version of it) and share best practices.
Check yourself: https://www.knxtutorial.com/
Ultimately wiring for KNX doesn’t take a lot more than just running a single extra wire through large sections of rooms since it’s a bus based system.
We worked on an hourly rate + cost of materials, rather than a fixed contract.
All the other home automation people I talked to didn’t really “get it”. This guy opened up to me about the importance of open standards from the first time I talked him and was happy at the concept of me programming the KNX devices myself, so I knew as soon as I met him that he was the right guy for the job.
I worked really closely with him (a daily catchup every day) in order to make sure everything was perfect.
I was really happy with the process, but it relied on getting a guy I could work really well with.