I think it's closer to $40-$50/year. The way it works in CA is that every book costs around $4 and the cost is equally split by the state, local gov, and the Imagination Library
Zip code 90740 has <800 under 5 yo kids. Total cost year 5 was something like $11k for the year.
This FAQ (via the neighboring comment) says the average rate is $2.10 per kid/month, so $25.20 per kid/year.