No matter what sort of system you're planning on installing, it's always good to talk to a custom installer first. Not only will they be able to advise you on what kind of system will best suit your needs, but they can also help to ensure that it's installed in the most efficient and cost effective way.
Like most things that make life easier, turning your house into a connected home comes at a price. Simple systems can be installed reasonably cheaply, but of course the more you’re able to afford, the more elaborate, secure and functional your system will be. Your budget is the only real limit to what you can do to make your house a smart home.