How much does it cost to unlock a iPhone 4S to any network?

I'm trying to get my iPhone 4S to work in family mobile from Walmart and I heard you have to get It unlocked so it could work but I don't know how much and where to get it unlocked, any ideas anyone, somewhere with a good price

You have an iPhone 4S, and you want to activate it with Walmart's Family Mobile plan.

First, you need to tell us what carrier your 4S originated from. Sprint, AT&T, Verizon, T-Mobile?
These iPhones are slightly different, basically it comes down to GSM or CDMA network hardware.
Next, is the iPhone committed to a contract, or is there a past due balance from a previous account?

Best scenario is AT&T, out of contract and they already unlocked it. You can take the 4S anywhere, domestic or overseas and use a different network sim to join a different carrier.
Same with T-Mobile - if it's out of contract, it's simple to unlock.

Verizon - maybe. It must be our of contract and free of any past due accts. The owner must be in good standing (paid bills on time for at least 3 months), and have a need for the phone to be unlocked.

Sprint can do a temporary unlock, but only for current account holders, Sprint does NOT unlock phones even if it's out of contract.

It usually does not cost anything to get them unlocked, but account activity may be required. Find out who the carrier is, and CALL them to discuss.

Hope this helps.