If you book the Trenton, NJ to Harrisburg, PA train within the next 7 days, you can find one way tickets to cost on average $42 (€37). However, booking your train ticket in advance gives you access to the best prices for trains to Harrisburg, PA from Trenton, NJ. Look out for train tickets for this route to go on sale a few months before your planned departure date to find the best deals.