How much would it cost for a train ticket from Harrisburg pa to oxon hill Maryland?

You would have to take 2 Amtrak trains: one from Harrisburg to Philadelphia, then another from Philadelphia to Washington, DC. The first train is about $30. The second can vary from $30 - 120 depending on the specific train (hard to believe, isn't it?) Then in Washington, you take the Red Line Metro train to Gallery Place, and the Green Line towards Branch Avenue, then whichever bus you need for Oxon Hill. It probably leaves from the Anacostia or Congress Hts. station.

HOWEVER: you can get from Harrisburg to Washington for half the price and in half the time by taking a Greyhound bus. It's only 110 miles on Interstate 83 and 95. You may have to change buses in Baltimore. If you take the train you are traveling about 250 miles and paying highly for the privilege.