What is the cheapest way to get liability insurance?
The answer depends on your state. Pick yours to see it.
For Washington drivers, the least expensive legal option is a policy meeting the state's minimum liability limits: $25,000 bodily injury or death for one person per accident, $50,000 for two or more people, and $10,000 for injury to or destruction of others' property. The alternatives to a policy require substantial assets: a liability bond or certificate of deposit of at least $60,000, or self-insurance if you own 26 or more vehicles. Driving uninsured can bring a fine of $550 or more.
Sources: WA DOL — Mandatory Insurance.