Not only is the Joomla software free, but when you download and install it on your host server it gives you a huge jump start in the building process. Coding takes time. Lots of time, but with Joomla you can build a site while doing little to no complex coding. That saves you an amazing amount of time. You can still pay someone tens of thousands of dollars to build a completely custom website for your organization. And perhaps you have needs that require that level of customization. However, there is a good chance that Joomla has a great extension for what you need.