Home Insurance – How is Costco so cheap?

Can someone give me some context if Costco Home Insurance is legitimately this cheap? They quoted me $750 for a 12-month premium. I said that I was looking into Auto as well.

Here are the details: we're buying a ~$350k house in Pearland. I have Auto with Geico, and they are quoting me $2,700 for $1k deductible, ~$100k in personal belongings coverage with replacement cost. Is there really this much difference in premiums?

Also – who's good for flood insurance, and do I need it in Pearland, TX?

Thanks all!