Definitely not an antoninianus as antoninianus have a radiate crown, this one has a laureate or diadem so it's a 4th century follis. It's most likely someone from the Constantinian dynasty, judging from the portrait alone I'd say Constantine himself. I can't read the obverse lettering and can't tell for certain what the reverse is so this is just me guessing.
As for value, 4th century bronze in such state is usually sold for about 1$ per coin if you can find a buyer.
I collect and deal in ancient Roman coin. In case you're looking for affordable ancient coins or need any help with the coins you already have send me a message.
