Expensive! F1 hybrids can run as much as $25000. And if your getting a savannah an F1 is where you should go. It's really cheaper just to get the pure serval but some people aren't into that for that some reason. Anything past F1 though just looks like an interesting colored house cat, sometimes you get lucky with F2's that act and appear more like their wild parents but most of them its just more and more house cat like which defeats the purpose of spending THAT much money when you can just adopt a spotty cat from the pound for the same effect.
You cannot treat them like any other cat though, they are very different, they need much more interaction and enrichment and if i'm not mistaken will need a more specialized diet.
NO! they cannot go outside on their own, this isn't even recommended with regular house cats.... they will go out and they will hunt, they are big enough and powerful enough that what they are hunting might belong to someone else (those annoying little toy dogs would make good prey) Also as someone else mentioned, most people will not know what it is and you risk loosing your expensive hybrid to an idiot with a gun who shoots first and asks later.
They are awesome animals but you have to go about it as if you were getting any other sort of wild cat. Obviously they are not like tigers or anything but you should still take all the same precautions and preparations in the beginning until you fully understand what you are into.