What should my minimum monthly Google ad spend be?

The minimum Google Ad spend is around $20 per day ($600 per month). This is because you can expect a minimum cost per click of about $2. This means you can afford ten clicks per day (10 visits to your website per day) which isn’t very many, and Google needs as much data as possible to learn. So, if you can’t afford to spend at least $20 per day for at least one month then don’t invest in Google Ads.