My experience (a few times) with front and rear glass replacement is that shops don't guarantee against glass breakage if they don't supply the part and they won't supply used. Working around the edges of glass is very tricky and a small chip can start a running crack. Old glass, in very sunny climates is brittle (another argument against used). However, the good news is that in some states, insurance companies do not question paying outright for new windshields if the crack is in your line of view. Check that first, and if the insurance company works this way, just take it in and get it done.