I'm just in the last stages of building my (Mianne-based) layout in a 12'x10' room. The layout is two levels with tunnels and mountains. My idea was to add four wired cameras, HDD/DVR, 1080, HDMI output, web accessible (with LAN plug-in), etc. - and I found one on Amazon. Web accessible seems like a good idea since the trains can be viewed on a phone or tablet, too. Kids love it.
Since I'm doing layout electrical now, wired cameras are all good.
Cost was around $160, shipped, with an Amazon coupon. The main DVR unit can handle eight cameras - but four should be sufficient. I'll output to a 32" mounted HDTV already in the train room.
I did spend another $12 to buy four 25' cables - to be used in place of the 65' cables that come with the unit.
Photos & additional reports soon, I hope.