A usage-based on-line solution is what you want - then all the backing-up is taken care of for you, and you only pay when you use it.
I'll declare an interest - I run a website which offer just such a service and our very own Cap'n PPRuNe has been a keen user. I won't break the rules by posting a link (e-logbooks typed into a search engine should do it).
I'm also a satisfied user of my own site - I lost my logbook last month (in Le Touquet - anybody found it?) and boy was I chuffed to have a full backup available...
Steve R