Typically in Seattle the price of a lease depends on the cost of the build out, divided by 36mths or the projected time before mandatory maintenance will be needed. It usually runs between $900-2000/mnth. Just keep in mind that Food Truck season up here is Apr-Oct and the leases usually don’t run years round. If you have anything owed in debt on the truck its best to look at selling rather than leasing a couple of bad months come fall and your leasee may decide not to pay and just walk away.
If the truck hasn’t been open long Selling out is best as you may have more expenses should they wreck the truck in a way that’s not covered by insurance. Like having your breaks or engine catch fire on the way to location. There is no specific coverage available for “in-transit” damage. Just once you are working. Had a friend have to close their business because of this, its now fun.