Zapier sells a plan level (Free, Professional, Team, Enterprise) combined with a monthly task tier. A task is one successful action; triggers and failed steps are not counted, and built-in tools such as Filter and Formatter are not counted either, according to Zapier's pricing page. If you go over your tier and pay-per-task is on, extra tasks are billed at a higher rate than the base allowance. The practical effect: cost scales with steps times runs.
n8n Cloud sells plans (Starter, Pro and Enterprise) with a monthly execution allowance (Business is a self-hosted paid edition), and every plan includes unlimited users and workflows, per n8n's pricing page. Cost scales with runs only. A workflow with 3 steps and one with 30 steps cost the same per run.
Self-hosted n8n Community Edition has no licence fee for internal business use. Your costs are a Linux server (a small VPS handles most small business loads), a database backup, and someone's time for updates and monitoring. At higher volume n8n supports queue mode with Redis and separate worker processes, which is more infrastructure to run. Features such as SSO, environments and log streaming sit in the paid Business and Enterprise editions.
The hidden cost on both sides is maintenance of the workflows themselves: an API changes, a Google Sheet column gets renamed, a token expires. Budget for someone to own that, whichever tool you pick.