Want to move from Okta to Entra but can't figure out how to do it without breaking everything

On Okta for six years, works fine. CFO noticed we're paying for Okta and already have Microsoft E5 and wants to know why we need both. Fair question except moving 2000 users and 80 apps from Okta to Entra without breaking things doesn't seem doable.

Each app is configured with Okta as IdP. Changing that means touching SAML settings in 80 different places. Some we control, some are vendor SaaS where we have to open tickets and wait. User MFA enrollment doesn't migrate so everyone re-enrolls. Groups and policies get rebuilt manually in Entra. Apps using Okta APIs for provisioning just stop working.

Running both during migration means users have two identities and we're managing the same access in two systems which is worse than staying put. Phased migration makes more sense but then App A is in Entra trying to talk to App B still in Okta and I don't know how to handle those dependencies without custom federation.

Consultant said six months and $200K. CFO thinks that's ridiculous for switching SSO providers. Doing it ourselves means months of after-hours work and probably breaking auth for critical apps at least once. Has anyone actually migrated IdPs at this scale without massive downtime or am I missing something obvious?