Google Provides a great calculator to help you predict what your cost savings will be by switching from Exchange 2007 to Google Apps Premier (Savings Calculator). The Google Apps cost savings calculator only requires that input two variables and then spits out your one time and ongoing savings. The two variables you need is number of employees and your IT Managers hourly rate. From this the Google Apps Cost savings calculator tells you what your upfront cost will be. In Google Apps this is the labor cost associated with migrating to Google Apps, this would include time spend planning, implementing, and migrating data. For Exchange this would also include the needed hardware (servers) that you would need to host Exchange on. Next the Google Apps Cost savings calculator gives you your annually cost for each of the solutions. In Google Apps these costs include licensing and administration labor costs. In exchange there is no ongoing licensing including but adds in infrastructure costs for maintaining hardware. For a 10 person company with an IT manager or consultant paid $70/hour the cost per employee for email in Google

Apps Premier is $379 while Exchange comes in at with cool $3,983 per employee. The upfront fees are also pretty staggering, Google Apps comes in at $1,354 while Exchange is $15,813.
The Google Apps Cost savings calculator is geared towards comparison with Exchange 2007 and using your existing IT staff. In many of the companies I deploy Google Apps for that have 10 employees they don’t have an IT person and instead have me do the deployment for them. In this case the labor is still only slightly higher and you get someone who knows how to deploy Google Apps with no hiccups. Many times even with an IT person on staff their time is better spent working with your industry or company specific software or processes that add value to the company.

If you are not looking at Exchange as an option you can still easily figure out your cost savings. Just look at the licensing costs of your alternative solution and use those figures instead of the licensing for Exchange. Either way the number will be dramatically on the side of Google Apps Premier for the simple reason that with Google Apps you have no hardware or infrastructure costs. Don’t forget that when thinking of hardware and infrastructure you simply don’t go out and buy the server and you’re done. You have cooling, backups, real estate, etc included in housing those servers.