Developers rent API docs, monitoring, secrets and webhook plumbing by the month for side projects that earn nothing yet. Self-hosted pay-once utilities cost less than one month of the SaaS they replace.
The tool this job usually means renting is Expensify, at $5–$9/user/mo — roughly $60 a year, every year. Snapreceipt does the job for a one-time $19 — running locally on your own machine.