Hello all,
Templar09, just to help clear up any possible confusion - I can clearly read the legend 'M ANTONINVS AVG TR ....'
This clearly identifies a Antonine Emperor, and not a Severan emperor. It certainly isn't Septimius Severus. There is no doubt in my mind that the coin in question is a sestertius of Marcus Aurelius.
With regards to the earlier comment on judging by portraiture, I need to stress that identifying ancients by portrait style is not a good idea and will lead to many conflicting, and wrong, identifications. Legends are the primary source of attribution, and should be considered first and foremost when identifying an ancient roman coin.
Take, for example, certain periods in Rome. In 69 AD, Rome went through 4 Emperors in one year. In that year, we see many examples of coins of emperors, such as Vitellius, where the legend clearly identifies emperor Vespasian. This occurred, in this instance, when the old portrait of Vitellius was used, with only the legends altered, until an accurate depiction of Vespasian came along. The same thing occurred when Vitellius seized power - there are many examples where his portrait, on the coinage struck immediately after his accession, where his name is used, but the portrait is clearly his predecessor, Otho.
Furthermore, in other eras, like the Tetrarchy, or the Constantinian dynasty, the emperor's busts are virtually interchangeable with one another, and if one was to obliterate the legends, it would be a difficult task indeed to identify the emperor by bust type alone. I would be more than happy to provide images and references and to discuss any of this information in depth with anyone interested.
For reference purposes alone, I would suggest the coin would retail for in or around $40-50 US. More if the reverse cleans up further, which looks possible, given the remaining encrustations.
Cheers!
Steve McBride, professional ancient coin dealer, VCoins.