Does family sharing cost me more

There is no additional charge for Family Sharing Apple TV+.

However if you want to share an Apple Music subscription, you need the higher priced Family plan to do that; the Individual and Student plans cannot be shared.

… to UPGRADE my subscription to the more expensive Family Plan.

You may have been misinformed. There is one plan that covers the regular Apple TV+ subscription. It is shareable with up to 5 other people (Apple IDs), at no additional cost. Other subscriptions may have special Family Plan options (e.g. Apple One, Apple Music), but not Apple TV+. Sharing the Apple TV+ subscription does require setting up a Family Sharing group with the prospect sharers (and managed by the organizer on their own Apple device).

Get Apple TV+ - Apple Support

About Family Sharing - Apple

Learn more about what you can do with Family Sharing - Apple Support

Set up Family Sharing - Apple Support

Add a family member to your shared subscriptions - Apple Support

Apple TV+ FAQ

Q4: Can I share with my family?

A4: Of course. Apple TV+ lets you share your subscription with up to five family members.

Sharing is done through separate Apple ID accounts, not multiple profiles on one account. That does make it a bit different for most other content providers. But Apple IDs are much more than just for a streaming service, so more separation (security) is needed.

In order for anyone other than you to stream on your AppleTV account you must *pay more* for the Family Plan as opposed to the regular plan(s)… I’ve been my own subscriber for years and wanted to simply add an additional account for when my sister is here — turns out the only way she can stream on my AppleTV+ account without having to use MY account profile is to UPGRADE my subscription to the more expensive Family Plan. That’s insane that we aren’t able to set up more than one PROFILE like ALL OF THE OTHER PLATFORMS…