It all depends on the complexity of the system and functionalities it is expected to provide. When designing the Grenton System, we did our best to optimize the individual module cost without sacrificing quality.
A simple smart-house system, offering basic functionalities, costs around 2000-3000 PLN. The system, with a full set of functionalities, can cost between 6000 and 12000 PLN.
You should keep in mind that even the simplest system will significantly affect your comfort and savings.