When you rent the locker, you pay $7.00. When you're done with the locker, return your key and receipt to the CM, and you'll get $2.00 back. I beleive that if you're going to another park on the same day, you can show your receipt and not have to pay again, although I didn't do this. In MK, the lockers are under the train station. In AK, they're on the left as you enter the park. I didn't use a locker in MGM or Epcot, but I'm sure someone else will know. I think they're all close to the park entrances.