If you mean the Verizon Trade-In program (see link below) then you will get about $230-$250 for your 4s depending on the memory capacity.
Subtract that from the full retail price (assuming you don't have an upgrade available) you would pay which is
$850 ( 64gb)
End result is between $400 - $620 depending on model.
I traded my iPhone 4S (64gb) at Best Buy Mobile and got $350. The only downside to this is it is in the form of a gift card. So it is only good if you plan on buying your iPhone 5 there.