The small project of extending the installation onto the attic was a chance to review the costs of 'intelligent' house components. Here is how much it all costed:
The UTP wire, despite the price, ended up being grate. It is not 100% copper, but for what I need - it is great. The wires were wrapped in a cellophane foil and an alu foil there is an additional wire for strengthening it all.
The DI/DO modules were used (from local ebay), but they work great.
What are the costs of extending the 'intelligent' system?
The cabinet costed EUR 150. In a traditional installation a EUR 50 unit would suffice.
The modules and UTP costed some 300 EUR. The relays EUR 130. If one started from scratch, a PLC would be needed. So a total of 1000 - 1200 EUR would be the total cost.