Anyone know of a place to get inexpensive patio dog doors?

My husband and I are looking to get a dog door for our sliding glass door, but the prices are incredible every place we've looked. Does anyone know where we can get one for around $100? We are living in San Diego County if that helps, but we are not closed off to ordering online. It would have to be a large size because we have a boxer lab and a full bred lab. Thanks in advance!