Alexandria Troas was an ancient Greek city situated on the Aegean Sea near the northern tip of Turkey's western coast. It was founded in 310BC, with Apollo the chief deity on their coins. You can see Apollo, an ideal beardless, athletic youth on both sides of this coin. He has been variously recognized as a god of light and the sun, truth and prophecy, healing, plague, music, poetry, and more.
The amazing coin in our picture comes from Gorny & Mosch in Munich where it sold recently at auction for 3400 euros, about $4400 US dollars. The coin is so beautiful and so rare, the price tag is not surprising. It is worth this much on the open market. The photo itself was produced by Lübke und Wiedemann, a digital photography firm in Stuttgart specializing in münzfotografie, the photography of coins. CoinQuest thanks Lübke und Wiedemann for use of their coin photo.
You won't find a coin in better shape than the one in the picture. If Declan's coin looks like the Gorny & Mosch coin, he can expect similar value. More wear would lower value. Damage, such as scratches, stains, holes, abrasive cleanings, nicks, gouges, and the like will lower value substantially.
If you have a coin like this to sell, a dealer would probably offer about one-half of retail value, maybe more.