Today

• Most sold workstations are either shipped with a operating system from Microsoft or the Microsoft operating system is installed when the the workstation is purchased. No matter how you view this, there is a considerable investment regarding licenses even for small companies. In addition one should expect to purchase upgrades as well, all thought special discounts may apply for these.
• Microsoft Outlook is a widely used client for professional users when working with mail, calendars and contacts. Outlook is mostly used with the Microsoft Exchange server as a backend. Outlook is the primary client for accessing Exchange. Both Outlook and Exchange are tied to the Microsoft operating system. Microsoft Outlook is part of the office suite offer provided by Microsoft and like the operating systems a license is require to use the office suite. The document formats used by the Microsoft office suite is widely considered a de facto standard for internal communication in companies.
• It's no secret that firewalls, antivirus software and spam filters are mandatory when you are running a Microsoft operating system. For several reasons, Microsoft has a history of being a favored target for malware. Must software for countering these threads on Microsoft operating systems requires a initial fee when purchased and an additional fees for continuous updates.

Software budget for a standard workstation:USD. ~$850
(MS Vista Business, MS Office 2007 standard, McAfee Internet Security Suite 2007)

Tomorrow

• Must Linux distributions are free so it wont affect your budget if you are installing on 10 or 1000 workstations. Must software in these distributions are provide under the GPL license.
• With the Brutus server from 42tools, clients running on any Unix like operating systems, programmed in the language of you choice, can access the full functionality of the Microsoft Exchange server. 42tools provide an evolution plugin allowing Evolution full access to Microsoft Exchange on pair with Microsofts Outlook client. Evolution and the evolution plugin from 42tools are provided free of charge under the GPL license.
• Openoffice is a multiplatform and multilingual office suite and an open-source project. Compatible with all other major office suites, the product is free to download, use, and distribute.
• As an offset, Unix like operating systems are more resilient to viruses that operating systems from Microsoft and you won't generally need antivirus software. Working in a mixed environment (with both Windows and unix like systems), there is a wide range of open source alternatives for virus scanning, spam filtrering and firewalls. These alternatives are comparable to many commercial offerings. Clam is a good antivirus scanner, SpamAssassin can filtrere your mail, while iptables is a effective firewall.

Software budget for a standard workstation:USD .$0;
(Linux, Openoffice, Evolution)