If you're doing anything more than toying around, this is not the case.

Using the API would have cost me $1200 this month, if I didn't have a subscription.

I'm a somewhat extensive user, but most of my coworkers are using $150-$400/month with the API.

less expensive than what? You can use CC on the $20 plan. If you're using the maximum of your $20 subscription usage every 4 hours every day, the equivalent API cost would be at least hundreds per month

There's a log analyzer tool that will tell you how much the API costs are for your usage: https://ccusage.com