there is a shuttle from Union station, but the last train back to Anaheim (Angel Stadium) leaves at 10:10, so no way you would be able to stay for more than two hours of the game. This would cost you about $50 bucks round trip. This could work if you are doing the rare day game.

http://losangeles.dodgers.mlb.com/la/ballpark/transportation/index.jsp?content=express

Might actually be the same price to get an economy rental car for 24 hours and pay the parking fee, there are tons of rental car companies right next to disneyland.