The kit comes with a fire extinguisher that is temperature activated. Plus, these aren't the hot running lithium ion batteries used in laptops. This is Lithium iron phosphate, it is much more stable. You'd REALLY have to abuse these batteries to get a violent reaction. In addition to this, there are safety mechanisms in place like fuses and breakers.
If it did happen, I'm sure insurance wouldn't cover that. I know the risks and I'm willing to take em.
Lithium is already the lowest cost per amount of total use you get out of the batteries. Their high cycle life makes them superior to others. If you think that other battery chemistries have a cost advantage in the long run you are mistaken.