Very simple local transport from Mandalay to Bagan is by boat. There are 4/5 different cruise. Government slow boat operate only Wednesday and Saturday which is very simple one, stop about 5 places and full with local passengers. Who want to have an experience traveling with local passengers should choose slow boat. That leaves at 06:00am from Mandalay and arrive to Bagan about 19:00pm.
RV Shwekeinnary, RV Malikha, RV Panorama are also express boat (day tour) between Mandalay and Bagan.
RV Pauk Kan, Ayeyarwaddy Princess, RV Yanabo, Road To Mandalay, RV Orcaella and RV Anawrahta are luxury cruise one night two days, or two nights three days between Mandalay and Bagan.