Can the Bayern ticket be used on weekends? what is the cost on weekends compared to the 28 euros on weekdays? Also where do you buy it? Can it be bought online?
Yes, the Bayern-Ticket can be used on weekends. It is even better as you do not have to wait until after 9am to begin your journey. The price is the same.
There is no advantage in buying the Bayern Ticket early. It can be bought at a ticket machine or over the ticket counter for 2 euros more.
You can read about the Bayern-Ticket on the official website .
The Bayern-Ticket is one of the German Länder tickets. Each German state, or Land (pl. Länder) has it's own all-day regional pass for 1 person (Single) or 2-5 people traveling together on regional trains. The Bayern (Bavarian)-Ticket is one of them.
See here for a list of Länder tickets and prices.