1
To find the price of the Personal Microsoft 365 subscription, go to this link:
https://www.microsoft.com/microsoft-365/buy/microsoft-365
2
With regards to switching form the Family version of Microsoft 365 to the Personal subscription.
If you had users associated to the Family version and they logged into Office with their own Microsoft Account, their data may be stored on their private Microsoft account, and if you stop the Family subscription, that will remove the 1TB of OneDrive storage each persona had on OneDrive, and they would only have the free 5GB of storage, so it would be best to backup their files first.
Only the Microsoft account used to take out the Personal Microsoft 265 subscription will have the same 1TB of OneDrive storage.
Then to switch to the Personal subscription cancel the Family subscription and take out a new Personal Microsoft 365 subscription.