I would suggest that you avoid buying SEP SBE. My information is less than perfect, but as a Symantec parenter I've been under advisement that SEP SBE will be discontinued at some point, with SEP Cloud being the product you should go to. I've attended several partner webinars over the past year or more that have all said this, but of course the marketing folks at Symantec have yet to learn to make things clear to the public (and that's not a jibe - it's very true, ask anyone who's been around a while).
If your deployment is big, like 100's of endpoints, continue as you can via CragV's advise or what not. But if you have the option, dispense with SEP SBE and go with SEP Cloud, also known as Endpoint Protection Cloud. Not to be confused with SEP SBE Cloud, which is not actually a product name but just the ocnfused verbage used by people wanting to differentiate SEP SBE on-premises server vs. the cloud management version that had come out a few years ago. Sigh, not to be confused with Symantec Endpoitn Protection, which is a full enterprise platofmr, which has it's own on-prem vs. cloud management structure.
I mean, if Symantec could just get their message out withotu so much puzzlement I bet sales would jump 20%. lol