Which solution would achieve the requirements with MINIMAL cost?

Explanations:

This option leverages daily EBS and RDS snapshots, which meets the 24-hour RPO. The Route 53 active-passive failover configuration ensures that traffic is routed to the disaster recovery region in the event of a failure. The EC2 Auto Scaling group with capacity set to 0 ensures minimal cost in the DR region.

Using an active-active failover configuration would incur additional costs for always running instances in the disaster recovery region, which is not necessary for a pilot light approach. This does not align with the goal of minimizing cost.

While this option uses ECS to manage tasks, ECS is over-engineered for this use case compared to using Lambda. Additionally, using ECS and Route 53 with active-passive failover would increase complexity and cost without providing additional benefits.

Although EBS and RDS cross-region snapshot copies are a valid solution, using an active-active failover configuration would lead to unnecessary cost for always-running resources in the disaster recovery region. The cost can be minimized with active-passive failover instead.