Well I had my windshield done last week for about $1500 total. My comprehensive deductible was $250. The company I used was local--Guardian Glass--and they did a fine job.

It cost me $1/mo to drop my comprehensive deductible from $250 to $100, and I may drop it to $0 assuming the cost is linear. If I get another broken windshield within 150 months then I've got my ROI. Based on how small the impact was for my last windshield, I'm pretty confident I won't go even half that long before the next rock break.