Probably a lot more than you want to pay
The 6S is about 3-4yrs old now. Not sure on what your willing to spend, but you should be able to find one at a pretty decent price on ebay or check with AT&T or Verizon. One of the large carriers may have one available.
Referring to walmart.com may help you more than I can.
Thanks! Your answer is awaiting moderation.