So you're basically going for the platinum deal there then.
I assume you don't have a bog standard semi worth £200-300k?
What I'm aiming for is something like the below. Some of it is already installed, other parts the house has been designed for but I will be installing at a later date, and some of it I haven't decided what I want yet.
Controller - Smartthings Hub (£100)
Lighting - spots and led strips I wouldn't include in the cost of automation, for example all my strips are being hard wired into the room lighting, so the overall cost of this part for automation is around 12 smart z wave dimmable switches - scenes being controlled by the Smartthings hub (set up using the app). I'd eventually like to have a controller built on the wall for downstairs as there will be multiple scene modes (cinema, party etc). Smart Switch costs are around 3x the cost of a bog standard switch. So uplift would be in the region of a few hundred quid (bearing in mind I'm in Canada so the exact cost is not directly comparable so not going to put an exact price on that as switches are different!). On the other hand as I mentioned earlier, that cost would increase significantly if you're including the entire cost of bulbs and light fittings, but I'd argue that's not really an automation cost as you'll need them regardless. A few electronically controlled blinds for downstairs
Access control - about the same . 1-2 electric locks for front and/or back door (I'm only going front and have keypad for garages).
Home security - I'm only real going to go for sensors/cameras in the garages, which is probably going to be a bit less than that, but for a full security system the price looks right. Whether most automatons want all that is debatable.
Heating and safety - again similar. Nest thermostat and protects along with moisture sensors in a few places and the mains cutoff (which is the biggest cost).
AV - where the big money is. We ended up going for separate sonos players rather than the amp and integrated speakers because the uplift was just too high, especially in places like bathrooms where you only really need a single play:1 at about 1/4 the price. All in all, as discussed prior.
All in all, after actually understanding what you want to achieve, an knowing you are going to be using a designed system £10k makes a bit more sense, especially if you're including lights in all that. You can do a similar system for a lot less however IMO and your average home automation project is going to cost significantly less
Just an aside, the main aim for my home automation is for the main room downstairs (see my renovation thread for some photos). I want to be able to turn the TV on in that area and have everything set automatically for TV watching (all lights but bar lights off, and bar lights (behind the seating area) dim to lowest setting , blinds draw and all systems automatically turn on - that will be acompished using a harmony remote and hub.) the rest of it is just an add on to that system. The locks, cameras, upstairs switches and water/fire stuff just integrate with the hub.