Adding Inverter

I have a similar question. WE also have no inverter and I am looking at adding one down the road. It will be a pure sine wave one. My concern is how to install it. I could install it and just connect to the batteries and plug things it at the inverter or have it installed where it functions all outlets. I can't see running many things on it besides charging some cell phones or computers. We've done good with out one so far.

My question is how much can I expect for installation of one to run all the outlets (labor only).