S.C. Code Ann. § 56-3-750: Fees for special mobile equipment vehicles.

For every special mobile equipment vehicle not exempt from the payment of a biennial registration and license fee under Section 56-3-120 the biennial registration fee is ten dollars for each vehicle having a gross weight of not more than four thousand pounds, and for every vehicle having a gross weight of more than four thousand pounds, an additional eight dollars for each additional one thousand pounds of weight or fraction over four thousand pounds.