Agencies pay per-seat and per-client fees that scale with their success. Self-hosted, pay-once tools replace per-seat pricing with a flat cost that margins actually survive.
The tool this job usually means renting is Screaming Frog, at £199/yr (~$250/yr) — roughly $250 a year, every year. Maptrail does the job for a one-time $19 — running locally on your own machine.