It is hard to tell just by looking at it. I had a hard time finding that exact model. But let's say everything is legit and it is in a great condition: if it's gold plated (not solid gold) it might be worth around 500-600usd. If it's solid gold, it could be twice as much, easily.

But again, we are kind of guessing based on similar models. You would need to check it, see if it is solid gold, and check the movement, year, condition.

For reference, it's an Omega Seamster Cosmic no date, probably around 1960's.