My iPhone 6 home button came out how much would I end up paying to get it fixed.?

If the home button simply "popped out" without any other damage to the iPhone from a drop or excessive pressure, Apple will probably repair or replace it for free (since the iPhone 6 would still be under warranty). Best option is to make a Genius Bar appointment at the Apple Store nearest you. If Apple determines that it is not a warranty issue, they would let you know the cost of the repair prior to doing the work.