SVN's branching is as free as gits - itsGit's. It's just a bit of housekeeping data that says where the branch starts, no changes to the stored files whatsoever. A 'copy' in SVN is like adding a symlink to a unixUnix directory. Note that the SVN branch will not require a network trip until you commit your working copy changes (but there's not much point having a SCM if you don't commit off-local at some point).
Note that a gitGit branch will also involve some housekeeping - like adding that tag internally - that will have to be stored somewhere when you commit. ItsIt's not a big deal at all, which is why itsit's called 'free'.