The obverse reads CONSTANTINVS IVN NOB C (Constantine Junior, noble caesar), which tells us that this coin shows Constantine II before he became emperor (which would have given him the title Augustus, which would turn up on the coin as AVG). The reverse reads 'CAESARVM NOSTRORVM' (Our Caesar) around a wreath with 'VOT X' inside. I'll let you try to google what that means, it will expose you to a whole lot of interesting stuff.
Beneath the wreath is the mintmark which seems to read (gamma)SIS, i.e. Siscia.
These things are actually really numerous because they produced so many coins during this period and circulated them so widely. Most late empire types can be had very cheaply.
I'm afraid so. It would probably go for a dollar or two, but the way it has been cleaned has removed the patina which destroys value. With the patina intact, the coin would have likely been much clearer and perhaps worth $5-10, as it is well centered and struck. Much more valuable for its history than its price tag.