That $49.3 is over 10 years.
That's about $5 million/year.
This equals roughly $56/ user/ year. (sounds pretty cheap to me)
I have been keeping tabs on this issue because, I'm the PM in charge of my Federal Agencies possible procurement/outsourcing of a new email/messaging system.
To the gent that can't understand why the USG is looking at the cloud computing alternative, it's because of funding and the recognition of technology advancements. It's an attempt by your Government to get into the current tech century. Client/Server based computing is so last year.
Outsourcing IT needs might be more cost effective for companies/agencies (Cost cutting). With all USG budgets being cut and the expectation for Gov't to do more, what would you suggest Gov't Agencies do? You will find it's extremely expensive to host an in-house email/messaging system then what you're proporting. Please take into considration that your local library doesn't need to maintain 99.9% uptime, the security needs of your local library can't compare with a Federal Agency, and the scope is completely different (Blackberry, 88,000 employees vs. your local library, etc)
And are you really suggesting the USG throw together a server with a freeware mail program like your library is doing? Really?