If you only have 550gb of stuff, just pick up another external 1tb drive for $70 and stash it in your desk drawer at work, or in your brother’s spare bedroom, or your drinking buddy’s garage (you get the idea). Swap it out with one of your master copies every few months to keep everything in sync.
With as little being added that infrequently, frankly online backup is probably overkill if you need to shoehorn it into working (ie you don’t just leave a drive plugged in all the time like Jlee suggested).