How much should I pay for iPhone 4s?

I want to buy a used on (16g, black) that looks new. I see prices from 250 to 500 dollars.Am I missing something here, why the disparity in pricing? This is my first smartphone, finally making the switch. I'm with Verizon, so staying with them would save a flash fee, otherwise I would have to calculate that into the cost of the phone.

Added (1). I'm leaving Verizon in six months when contract is over. It will be cheaper for me to go to prepay and buy phone than stay on Verizon's overpriced system. Even if the phone cost 500 dollars, it is still cheaper to leave Verizon and go prepay.

If your contact is over, you can get the 4s for &99

Extend your contract for 2 years and they will pick up most of the cost… It makes sense to do that.

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