I know enterprise does car rentals on the weekend for the low low . . . For example . . . I just reserved a 4 day rental for this weekend for 80 bucks on a full size after all the taxes . . . so it may be an option for you.
As far as shuttle buses go . . . I have no clue, but I know the 2 bus in Broward runs right next to Dolphins stadium . . . some hood over there, but it may be a smart way to go on game day . . . and u save on parking and gas.
Still always nice to have a rental in hot South Florida.