In general it is not expensive. In most cases you can either load balance across two regions all the time or have a fallback region that you scale out/up and switch to if needed.
IMO, going multi AZ or multi-cloud adds a good amount of complexity.
TBH I don't care if last.fm doesn't work for 8 hours a year, that isn't a big deal. My bank? Yeah that should work.
Servers are easy. I’m sure most companies already have servers that can be spun up. Things related to data are not.
And no, data replication or load balancing is not easy, nor cheap.
* Automated. * Scoped to business critical services. Typically not including many of the 3rd party services. * Uses data replication, which is a feature in any modern cloud. * Load balancing, by DNS basically for free or a real LB somewhere on the edge.
If you fail at this you probably fail at disaster recovery too or any good practice on how to run things in the cloud. Most likely because of very poor architecture.
It's easy to replicate multi-tenancy for RDS since it's built in. But it's not cheap. It's double, triple the price.