Okta has a free tier for 1000 active users/month (not 1000 logins but 1000 separate users logging in as many times as you'd like). After 1000 it's cheap as heck. https://developer.okta.com/pricing
Edit: Equivalently any SAAS sucks since they may in the future raise their prices is your argument.
This is a very real argument though? Reliance of a core part of your saas on another company, who is liable to change prices at any time, is a real business risk. The Google Maps API pricing change is a big example.