By 'bobtail insurance' some companies and people mean bobtail liability and phisycal damage (comp and collision) together. So to avoid confuse in communication we recommend using term 'Bobtail Liability Only'. Majority of insurance companies doesn't offer Bobtail Liability Only policy as it's usually included into Truckinig Liability or Physical Damage (Comp and Collision) policy and not sold separately.
Prices from major insurance companies:
NASTC (844.264.8500) - $35 per month or $420 per year (with $35 initial deposit). 2 years minimum driver experience.
NITIC (800-726-8376) - $244 one time payment for each truck and then $47 per month.
Commercial Truck Insurance Head Quarter (888 459 0717) - $244 per month.
Progressive - doesn't offer Bobtail Liability Only.
GEICO - doesn't offer Bobtail Liability Only.