If you require insurance against total site loss then a remote data backup solution makes sense - however, don't be fooled that this will get you up and running again quickly. For a full DR solution you need to be replicating at the application level to remote servers using SQL Log Shipping or for Exchange something like Neverfail or Double take. Relying on local off-line servers does not protect you against all eventualities. The cost of remote data centre hosting and links depends on many factors but in my experience can work out cheaper than a remote backup solution especially when amortised over the longer term and will give you much more flexibility.