The email I received from them this morning claims that this will be cheaper for 96% of users...

I have cron jobs on several github projects that runs once a day and I have never been charged anything for it (other than my github membership). Should I expect to be charged for this?

I would think that majority of users does not use GitHub actions at all or have very light infrequent usage so that would be true. I think with my personal project I have never exceeded the resources they give me as part of personal pro subscription.