Remember that there's a huge difference between files you need to read and write at any time with low latency and backups which happen at larger intervals and read infrequently, with looser latency demands. For backups, the service to compare is Glacier, which is about an order of magnitude cheaper.

What I'd consider is essentially the Crashplan model: P2P / external backups locally (i.e. full LAN speed) and an off-site replica which can be cheaper and slower as long as you have a high confidence that it'll be available eventually. This way normal operations are fast but if the building burns down you're covered and presumably have higher priorities than waiting for a restore to run.