SeVastopol

Sebastopol is also correct: https://en.wikipedia.org/wiki/Sevastopol

That's what I thought, but I wasn't home so I couldn't look it up. We also have a city in California by that name with a B.

Sebastopol is the original name, because it was founded by the Greeks and their "v" is transfirmed into the Russian "б". Like, for example, Biblia is pronounced with "v" in Greek while with "б" in Russian - Библия.

Good point!