These threads are always kind of misleading. Condition and location are really important. I've seen them go from less than $300 to over $1000. And when you buy a $300 Q*Bert, you're likely to get something that needs some work and you'll end up sinking more money into it than you paid for it. By the time you buy a CPO, sideart, paint, other parts (and don't forget shipping on all those items) and then dump hours and hours of labor into it, it ends up costing you. If cosmetics don't matter to you, then I wouldn't pay more than $500. But if you want a nice minty Q*Bert that doesn't need any work, you wouldn't be unreasaonable pushing $1000 or even more depending on where you are located and how much you want one.
It's UNLIKELY that you'll be getting a mint Q*bert from this guy though so $500 might end up being the right price, or even less than that.
And remember that $300 in a location far away from you might as well be $700 because it needs to be shipped, and shipping is expensive.
I'm not saying I disagree with the other posters here, but I think it's a little more complex than just saying "Q*bert is worth $500" and then having you go away feeling that paying anything more than that is a ripoff or that if you pay less than that then you've somehow made a great deal.