I really fail to see the logic of some of the commenters. Having looked into this in the past, Office 365 pretty much always comes out cheaper than SBS. And if your on-site premises internet connection has reliability/bandwidth issues, the absolute last thing you want to be doing is running your Exchange server at the end of it.
The concern expressed by Exchange system administrators and those implementing Exchange for clients with regard to bandwidth generally has nothing to do with the Exchange server's interaction with the Internet (e.g. sending and receiving SMTP messages) and more to do with the Exchange server's interaction with on premesis clients such as Outlook.
An Exchange server can be send/receive mail over dial up if need be and it wouldn't be a problem. Outlook, on the other hand, has a well known and understood history of experiencing noticeable performance degradation when talking to an Exchange server on the other side of a WAN link. This is why Microsoft implemented RPC over HTTPS for Outlook and why they also added cached Exchange mode (which has performance, reliability, and stability issues of its own).
If you have a slow (or even a fast with high latency, like cable) Internet connection, the very first place to consider an Exchange server is on premesis. System administrators don't care about bandwidth for exchanging SMTP messages with other mail servers on the Internet, that problem is solved with sensible configuration. Management, however, doesn't like when someone clicks File -> Open -> Other user's calendar, and it takes 30 seconds to open and a balloon pops up saying "Outlook is retrieving information from the Exchange server..." or their OST file gets corrupt because when syncing, for whatever reason, Outlook couldn't handle a high latency connection very well, hangs on the PC, and needs to be end tasked. Or someone logs into Office365, updates the global address book and everyone has to wait til Outlook decides it's convenient for it to update the locally cached address book, and then when it eventually decides it doesn't feel like it, the sysadmin needs to be called in to delete the local oab to force a recache.
Sysadmins aren't resistant to Exchange in the cloud because it threatens their careers. They are resistant to it because Outlook blows at talking to an Exchange server at a cloud provider. Management teams who are resistant to the cloud, however, have reasons that have absolutely nothing to do with the sysadmin's career.