> Okta for example charges $2 just for sign in: https://www.okta.com/pricing/
You're looking at the wrong product, $2/user/month is for their Workforce Identity Cloud, so auth for employees, not end users.
For a comparable market segment, Auth0 (acquired by Okta) which serves the B2C market charges significantly less [1]. Taking the B2C Professional plan at 1000 MAU which has the highest pricing per user due to lack of volume discounts costs $240/month for 1000 users ($0.24/user/month). Scaling up to the limit of publicly available pricing, at 10000 users Auth0 will only charge $0.15/user/month.