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 ChartMogul / Baremetrics, at $50-100+/mo โ roughly $600 a year, every year. Clientdesk does the job for a one-time $39 โ running on infrastructure you control.