To estimate value the coin first needs to be identified as to type, condition, denomination, mint, and comparable sales prices. For starters, I'd guess this is a 'follis' from the Constantine I, the Great Commemorative series of 307-337.
Searching Google's "Completed Listings" will give you an idea of current values for similar (but not necessarily the exact same) coin. A similar coin--but in 'extremely fine' condition is coming up for auction on December 7th. You may wish to follow up on that auction here: https://www.numisbids.com/n.php?p=lot&sid=938&lot=802
Don....
A buddy at my work got a bunch of these romans when he was cleaning out an estate and the family didnt want anything in the house they just wanted it cleaned out.
The obverse will read: VRBS ROMA (City of Rome). In the exergue on the coin's reverse, the mint mark will be shown (though I can't read it on your coin). The mint will most likely be from either Lyons, Trier,Arles, Siscia, Nicomedia or Alexandria. I'll keep looking.
Don.......