Now I looked on Bahn's site and was curious about trains that left before 9am (so I could get down there earlier) and it seems there are some and that I can get a Bayern-Ticket (return Journey) for 48.50€. So I am confused about this since I thought the Bayern is only good after 9am.
Yes, Bavaria Ticket is valid only from 9am on weekdays and you can't change that. What DB website shows you for 48,5 euro is basically a combination of full fare ticket (25,5 euro) Munich-Fussen for your outward trip starting before 9am and actual Bavaria-Ticket for 23 euro for your return leg, so 25,5+23=48,5
I'm just trying to see what the cost would be if I left on a earlier train before 9am.
Well, earliest direct train to Fussen leaves at 7:53am, so basically you don't need to pay full fare for the entire trip here, but just full fare ticket till the station this direct train passes at 9am (roughly half way between Munich and Fussen). While for the rest of the outward journey and for the entire return trip you can just get 23 euro Bavaria Ticket.
In practice such trick would look like this - in Munich you buy Bavaria Ticket + standard ticket Munich-Kaufbeuren (from this station earliest direct train Munich-Fussen departs exactly at 9am) for 17,4 euro, thus in total costs would be 23+17,4=40,4 euro. Then board the 7:53 train and until Kaufbeuren you show conductor you full fare standard ticket, while after your Bavaria-Ticket
Otherwise, choice whether to pay 40,4 euro and have an extra hour or pay just 23 euro is totally yours