@Ailish McCarthy For a single-node cluster, there are no additional costs associated with re-indexing, since we only charge for outgoing bandwidth.
For multi-node clusters (HA and SDN), the data needs to be replicated to multiple nodes, and that is counted as outgoing bandwidth. But bandwidth typically costs only $0.09 per GB, so it's usually not the most expensive component.
So you should be good to re-index regularly. I've seen users do a full reindex as often as an hour in some cases.