How much does sending an alert actually cost?

Yes, proportionally — each round of escalation to a new recipient is its own alert send. That is by design: IRIS bills for what actually went out, and the per-recipient frequency cap exists specifically to stop an alert storm from silently running up cost on messages nobody reads.

On the free trial or a paid plan, sends stop once your balance is exhausted rather than being throttled or degraded beforehand — you top up with a credit pack or move to a higher tier to keep sending.

Yes — direct sends draw from the same per-tenant credit balance at the SMS rate, itemised separately on your usage report. The payment model differs, though: the SMS-sending API is prepaid-only (no subscription), and only messages actually sent are charged — sends suppressed by the frequency filter or rejected by the destination allowlist never debit. Alert Management, by contrast, is sold as a per-user plan with bundled monthly credits once paid tiers launch.