Upgrading iCloud storage is .99 cents/month.. I only need the 50gb I get from .99 cents/month to backup.. what if I cancel the auto renewal ?

You can cancel whenever you wish. 

Apple give you a limited amount of time to download everything you wish until you’re using no more than the free allowance. After that, Apple will just delete files until you’re back within the free limit.

Their policy is pretty well standard compared to other Cloud-based storage services.

If you don’t want to pay for online backup then backup to external hard drives connected to your host computer and for security keep at least one additional identical backup hard drive which you store separately to the first one. That’s so that if a disaster occurs such as fire or flood or plain old drive failure then it’s less likely to destroy both backups.

If you cancel, you run the risk of losing everything you don't have backed up somewhere else on day at whatever time you'd be considered in default of the iCloud terms you agreed to.