The 2023-2026 model price war — and why your cost model is already obsolete — step 7 of 8

Write cost_per_user_month(usage) that takes a usage profile dict and returns the projected dollar cost per user per month as a float rounded to 2 decimals.

usage has four fields:

• messages_per_day: int — how many model calls per day for this user
• avg_input_tokens: int — average input tokens per call
• avg_output_tokens: int — average output tokens per call
• model: str — one of "haiku", "sonnet", "opus"

Use these 2026-real prices per million tokens (input / output):

• haiku: $1.00 / $5.00
• sonnet: $3.00 / $15.00
• opus: $5.00 / $25.00

Treat one month as 30 days.

Two demo users run. Expected output:

power user (haiku):  $1.72/user/mo
pro user (sonnet):   $4.14/user/mo