Since we're on the subject and it has been seriously necrobumped...
I install Crestron and I buy almost entirely via eBay. This means that a serious system costs me well under dealer pricing during installations and I give a one year warranty on the product. The final cost can be in the same price range as far lesser expensive systems, but at the end of the day 'Fully Blown System' means that there is a LOT of other stuff going on and it isn't Crestron which is the cost.
20 pairs of good in-ceiling speakers - $3,000+
Amplifiers for all of those speakers - $6,000+
Touchpanels in all the rooms (WHY?) - $20,000 (stupid)
Keypads in all the rooms instead $3,000
iPad Control - Buy an iPad, add $99
Switching & preamps - $1,000 (or so)
Sources - How many? Call it 8. $2,000 maybe a LOT more.
Lighting system - $10,000+
Security, sprinklers, HVAC, pool, etc., etc., etc. - $200,000+
For all the money that is spent, it is not Crestron or Savant, or Control4 that the money goes to, it is the quality components that go in everywhere else. A good theater seat may run $1,000+. You may need 8 or 9 of them. The full theater build out without one piece of electronics can be $25,000+ fully decorated quite easily. Then people may gripe about a $3,000 projector and $5,000 in speakers and $2,500 in electronics in that same room. Go figure.
Right now, no company I know of does HDMI distribution better than Crestron. Nobody. Extron, AMX, and Purelink come close. The rest don't come close that I've seen. So, the price of that type of quality is significant, but in line with the other major players (AMX/Extron/Purelink). Think $20,000 for 8x8 HDMI switching. Double it for 16x16.
Bells and whistles? Yeah, that'll cost you. But, a full system in a home that size with just A/V distribution, maybe a bit of lighting and more general components? $20,000-$40,000 is certainly realistic depending on how easy the wiring is. The labor for wiring is a major charge and varies wildly depending on the home.