The business data does not have to be located in the same building to be viewed or updated. Central shared resources such as file servers, print servers and databases can be located in a central building while everybody having access to them.
You should be able to expand your existing LAN to another physical location in couple of hours by just connecting two or multiple LAN sites together. This should be done securely and without having to pay for telecom companies or to have to install any additional cabling.
With wireless bridging, there is no need for expensive cabling or costly fixed telecommunications links.