What is a FAIR price on used iphone?

Just out of curiosity what is a FAIR price on a used iphone 4 (NOT A 4S)
in relatively good condition (screen not broke, fully functional, minor cosmetic wear exc)

I've seen used iphone 4 go from 150 (even for a broken one) upwards to 400+ for pristine (still used) condition.

The iphone 4 is still a relatively good working model, I've seen people get these for prices below 150 up to 300. I would honestly say not to pay more than about 120 just because the iphone 4S and iphone 5 is already out, and I'm sure apple will be releasing another new phone in about another year or two.