Here's a nice article from JAMA explaining why buying insurance across state line doesn't help very much
https://newsatjama.jama.com/2016/10/19/jama-forum-those-pesky-lines-around-states/

Tort reform has been shown to lower costs by a couple percentage points but not much more. The only way to control health costs to patients, businesses, and government is to reduce some of the profits earned by all of the providers, pharmaceutical firms, insurance companies, medical centers, equipment manufacturers, etc. in our health care system. It's hard to achieve that without a single payer system.