Old (Roman?) Coin- Details/Value

Clearer pics would be nice to confirm, but extrapolating from your description, the best fit is a bronze coin of Marcus Aurelius. On the obverse (portrait-side) is the emperor named there; there were several emperors who put the name "Antoninus" on their coins, but only Marcus Aurelius issued coins with "TRP XXVIII" in the obverse inscription as well.

ON the reverse, the seated figure is Jupiter, holding a little figure of Victory in front of him.

The denomination is uncertain. If you can tell us how large your coin is, that would help, since this design was used on the large sestertius and the smaller dupondius; on the latter, the emperor wears a "radiate crown". I can't see the portrait on your coin clearly enough to tell if he's wearing a radiate crown or not.

I found both of these options using the Wildwinds partial inscription search tool. It's excellent for helping to identify ancient coins on which you can only read a few letters.

Value depends on condition, and we'd need to see better pics of your coin to judge that. But the one in the link sold for $341 at auction some years ago.