This up-pricing is so short sighted. Offering SSO is a whole user creds mangement flow you don't have to write, secrets you don't have to store, and password theft PR you don't have to have.
So it's cheaper, less risk, and reduces friction to join.
If I'm doing a professional SaaS today, I don't store passwords. I use login with (Microsoft, Google, Apple with a user flow for FIDO Alliance passwordless) and SSO. If consumer, I'd use those and add Facebook. Gaming, Discord. Etc.
So you're looking to pay $1000 per user per year?