Is a used iphone 4 16gb for $200 worth it?

Its att so I need to pay to get it unlocked, how much do you think it will cost to unlock it so it could work with any carrier?

No!

It is a three year old phone and so old it is eligible to enrol in day care!

New phones have NOT gone out of fashion any/all phones that came out in 2010 have already been eclipsed. The IP4 is no exception.

Both the Samsung Galaxy Ace II and the Lumia 620 have easily pass the IP4 (IE are best described as mid range, new so won't require unlocking.

Here is an earlier answer