When Lightroom backs up the files and folders, each time it creates a new one. That is a lot of MB. Are you keeping the old files? Or can they be deleted?
I go in and clean my backups on occasion. When I do, I generally just keep the last couple. AND - I also keep backups of my backups on an EHD. Just in case.
For the Lr backups, which in my case are stored in My DOcuments, I keep 2 iterations and back up 2-3 times a week my entire My Documents to an EHD, then sync that with my second system.
I use Synctoy to do this for the last year or so, and have had no problems and feel that having the catalog backed up to 3 seperate hard discs is secure enough.