Here in Europe a zwave multisensory will cost 50€ each (ouch!) while a wired sensor will cost about 30€ each.
But you have to add the biggest cost: building works. Because I don’t want to have all the wires exposed…
This cost here in Italy is very high, because we have bricks every where…
So every electrician or bricklayer I met suggested me to use a wireless alarm system… 
Do you think a z-wave alarm will be as reliable as a traditional alarm system?
I think so from what I have read and seen z wave can be pretty reliable and has the ability to for mesh networking. Having lived in Italy I know the walls can be pretty thick and oddly wired so I would recommend z wave. However range especially in older Italian buildings like “centro storico” old might get to be hard as those are usually thicker walled. I know you don want exposed wires but what about the plastic conduits they cover the wires, and you could run them along the floors. Just a thought.
I have same problem as you for most part (concrete/brick + metal). This makes wiring mostly impossible and wireless signal very poor. For example 2.5ghz wifi cannot penetrate to area 25’ away with only 1 wall separating. Complete deadzone for cellular. I am starting Zwave device install to that area next week so will let you know result for reference
I first try multiple RasPi HA install with connected sensor but realized overhead of basicaally managing multiple server was too much. Also this still needed wifi repeater. I now roll this back and start move to Zwave which I feel is 100%reliable if battery monitor automation is added.
I plan Zwave motion in every room so this cost can get expensive. This is not for security need but people tracking need. Most home can use door/windowsensor for entry points and 1 or 2 motion to cover main movement area.
I install alarms many years and Zwave was always good. Just didn’t look as good since sensors were bulky once upon a time. Fibaro makes tiny door sensors and probably others have similar so ok now