Nero?

I don't know what you paid for it but you can see what similar coins have sold for in recent CNG auctions. I've linked to the e-auctions results page for search terms "Egypt, Alexandria. Nero tetradrachm, eagle".

The coin is not as rare as the lack of comps might suggest-- these types of Alexandrian tetradrachm are often lumped together in groups and sold without much in the way of specific description.

Alexandrian Nero tetradrachms are abundant. I picked up three while at the ANA World's Fair of Money in Chicago last month. You can see them and many other Roman Egyptian coins on my website, link in my signature line. I have many more coins to add but photographing and loading them takes time.