Check out NortonDNS and DynDNS
(see http://msmvps.com/blogs/bradley/archive/2012/03/08/7-days-until-the-opendns-ends-for-most-smbs.aspx )
If you do decide to go back to root hints remember that ALL Windows 2008 r2 boxes have DNS resolution problems with root hints and thus all Win2k8 r2 need to enable a registry edit of – http://blogs.technet.com/b/sbs/archive/2009/01/29/cannot-resolve-names-in-certain-top-level-domains-like-co-uk.aspx
Dyn.com clearly states it is free (at least today), i do not see what norton cost. When clicking on their business version one has to sign up.
Do you know the guestimated cost for norton for the 1-50 range?
Also, check out McAfee SaaS Web Protection. This is the service I moved to along with their Email security service. It works great and has even more granular filtering than OpenDNS.