Not all open source software is available for free, neither is even the free software without cost in management. With any choice of operating system and software packages someone will have to be responsible for maintaining the system and applying security and product updates. Someone will have to be responsible for fixing things when they go wrong, regardless of the reason.
Most open source operating systems are low-cost or free for educational use. They come with a variety of useful administration tools and user applications. All can be setup to have total, restricted or no access to the internet. However, these operating systems are very much unlike Microsoft Windows or Microsoft NT from an administration point of view and these differences often make it necessary to either employ a system administrator or contract the system administration out to a qualified professional. Many of the companies whom make up OSV are happy to provide on-going support in this manner [link to sysadmin page].
Hiring external system administration may appear to stretch the IT budget. Keep in mind, though, that if you use an open source operating system, you won't have to pay large licence fees for each computer's operating system. What is more there are many open source software packages that also come at lost cost but provide equivalent functionality to the propriety alternatives.
For example, for word processing tasks:
A free multi-platform office productivity suit. It includes the key desktop applications such as a word procesor, spreadsheet, presentation manager and drawing program.
A free word processing program similar to Microsft Word.