Cost¶

The expensive mistake is usually the path, not the payload.

Classic multi-bus bills by the event and again every time you hop to another bus. The enhanced bus bills ingress when you publish and egress when a Subscriber actually receives data. RAM share itself is free — you pay for traffic and retention, not for the invitation.

Rates below are from EventBridge pricing (retrieved 26 September 2026). Check the live page before you budget.

Two meters¶

Classic still thinks in millions of events (64 KB chunks). A custom publish is about $1 per million. Same-account delivery is often free; send that event to another account’s bus and you typically pay another $1 per million for the hop.

Enhanced meters gigabytes, rounded up to 1 KB per event. The public example uses roughly $0.18/GB ingress on the first tier (then $0.12), and $0.05/GB egress per subscription that gets the event. Keep events for longer than the included default and storage shows up (example $0.08/GB). Dedup and JSONata are optional — leave them off and they cost nothing.

So the comparison is not “which table looks nicer.” It is whether your bill grows with how many times you hop or with how much data you publish and deliver.

Who gets the invoice¶

On classic hops, the sender often eats cross-account delivery. On the enhanced bus, publishers fund ingress and each consumer funds the egress for their own Subscriber. The bus owner can see delivery volume per consumer account (EventsDelivered / EgressBytes with SubscriberAccount) — useful when you want chargeback without inventing hop accounting.

A hop story (classic)¶

AWS’s own classic walkthrough: 10 million custom events into account A, half of them forwarded to a bus in B, then to a service in B → $10 to publish + $5 for the cross-bus hop = $15. The last hop inside B is free.

Now imagine three consumer accounts each needing that full 10M stream as a hop. You still pay $10 once to publish — and about $30 more just to move the same events across bus boundaries. Topology did the damage.

Same volume, one bus (enhanced)¶

Keep the 10 million events. Say they average 2 KB → 20 GB in. Three Subscribers each take the lot → 60 GB out. No evaluation features:

Against the ~$40 hop sketch above, most of the gap is “we stopped paying per hop,” not “events got cheaper by magic.” Filters set egress: only matched events meter out. A wide or missing filter means every bus event can hit this Subscriber’s bill; tighten the pattern and egress drops with it. Retries and long retention add lines — keep them in mind, don’t ignore them.

Numbers move with size, selectivity, and region. Treat this as a shape check, not a quote.

When cost points which way¶

Stay on classic when you are mostly one account, you are not building a hop chain, and per-event pricing is already boringly cheap.

Lean enhanced when several accounts drink from the same stream, when every new consumer would mean another hop ticket, or when you want publishers and subscribers on separate sides of the bill. Skip paid evaluation features until you need them.

Cost will not save you from a bad blast-radius choice — that is still Patterns. It will tell you if you are about to pay for plumbing instead of events.

This lab¶

A few verify puts, one FIFO Subscriber, 7-day retention, no dedup or JSONata. Expect cents, then tear down (Demo).

Full source list: References.