How much would it cost to replace a lost iPhone 4?

How much would it cost to replace a lost iPhone 4?

Added (1). Forgot to add some stuff. My upgrade was this coming Christmas (we have a 2-year plan).

Added (2). I'm with AT&T.

It shouldnt be that much but depending on what company, if they no longer have the iphone 4 they will boost you up to a iphone 4s, should be below 100 considering the iphone 4 is older.

IPhone 4S are not in production and when you upgrade, you'll get iPhone 5C for free if you take the upgrade.