Mo. Rev. Stat. § 430.080: Lien on chattels for labor and materials.

Every person expending labor, services, skill or material upon any chattel at the request of its owner, authorized agent of the owner, or lawful possessor thereof, in the amount of twenty-five dollars or less, shall have a lien upon such chattel beginning upon the date of commencement of such expenditure of labor, services, skill, or materials for the contract price for all such expenditure of labor, services, skill, or material, until the possession of such chattel is voluntarily relinquished to such owner or authorized agent, or to one entitled to the possession thereof.