Importantly at the moment there is also a significant jump in reliability when you have these professional installs ( Control4, AMX, Savant, Crestron), Some of this is down to the hardware, in-particular the substitution and use of radio linked devices to ease retrofit situations and some just the experience and expertise of the installers.
The major cost differential is however the time based labour involved, which in the home install markets is just ignored and absorbed by the hobbyist. This can be a really significant time when you actually add it all up - especially in hindsight when things constantly keep going wrong and need remedying. If you have to apply a commercial time rate and travel to that it becomes horribly expensive. Sometimes these issues are down to inherent product bugs but the higher end products are orders of magnitude better tested and near 100% dependable, and correspondingly more expensive. However , doing it yourself allows for great flexibility and the ability to change the operation / upgrade without significant costs , rather than locking yourself in to an expensive upgrade with your installer. None of the configuration software for these higher end products is available to the end user customer. This is a most significant issue if you do step up to a professional install.
I doubt that there are any ‘people with technical expertise’ who would recommend a SmartThings based system currently as it still has too many teething problems which inevitably will result in an unhappy customer. ST will get there, although it’s journey is surprisingly slow at the moment. Fixing the scheduling will be a huge step as that’s a fundamental flaw, but that is being worked on as top priority.
Unfortunately decent home automation for the truly non technical is not easy or even really achievable currently. ST has set out to try and offer that type of solution but it is still in it’s infancy. The hub is offered at an extraordinary low cost although third party sensors are probably more expensive than they need to be for mass adoption. Regardless the belief that you can create a full and dependable HA system without technical know how for a few hundred dollars is fallacy (currently) but in time ST might be just that product.
The other thing I would add is that investing in HA will be a continually evolving project and it’s addictive, your needs and ideas will change very frequently, perhaps weekly and early on you will make uninformed decisions that you will want to change. In order to satisfy your new found interest you will need to be able to understand how your system works, where it might be letting you down and why and how to fix and enhance it. This inevitably requires some technical knowledge currently but SmartThings and this community is a way to ease into that although it’s a contradiction of frustration and elation currently. Being reliant on paid help will be problematic. Unfortunately the need for coding and other tech aspects is more prevalent in the UK as fewer devices are supported out of the box.
Every manufacturer knows this market is large and growing but it’s proving problematic. There are others trying to fill this middle gap between the hobbyist and the professional systems - Loxone being perhaps the most obvious. As ever a well thought through specification will reap dividends although I realise people often don’t know what the system is capable of or even what they actually want at the time they first jump onboard.