Switching cost of Micrrosoft to Linux

In the era of current soft economy and less IT budget and spending,if you where to decide to implement a Linux Operating system in place of a Windows System in your establishment, what will be the leading reason influencing your decision to do so,secondly what will be impact in terms of switching costs(advantages or disadvantages) of doing just that and lastly what will be the monterary impact of such a move in approximate dollar figure.