There is very limited free parking if you can find a spot on the street. There are meter spots, 15 min is $0.25 or you can park at renessaince garage on campus. It is $6 for the day on the weekends at Renessaince. Renessaince Garage is probably the best option if you are going to drive in. There is also a garage right by the arena, Gaisnborough garage, but that will cost about $20 or more for the day because they usually charge a flat event parking fee! Yay Boston Parking!
Directions and a campus map can be found here:
http://www.neu.edu/campusmap/
By T:
In order to get to Mathews arena you can take the orange line to Mass ave or the Green line
E train to Symphony. Mathews arena is located on the corner of Mass Ave and St. Boltoph St. Parking at T-stations is about $3 usually but you'd have to check with the one you want to park at. Riverside T stop is right off of 90 but its a long T ride in to get to NU because you have to transfer lines.
If you have any more questions about parking feel free to get in contact with me via email or PM.