We purchased a new dog door from Home Depot. After much debate, this was a must. These doors aren't cheap and our sliding door happens to be a massive 96" tall so we had to special order the door.
At Lowes the door was $305. Home Depot had it for $255. Clearly, Home Depot was the winner. The reason I felt the investment was somewhat risky was because we really didn't know if our stubborn pooch would actually use it.
Thankfully, after a few training treats, Morgan found his new haven on our balcony.