Section 2A. It is hereby declared to be against public policy for any employer to employ any person in agriculture and farming in this commonwealth at an oppressive and unreasonable wage and any contract, agreement or understanding for or in relation to such employment shall be null and void. A wage of less than $8.00 per hour in agriculture and farming shall be conclusively presumed to be oppressive and unreasonable, wherever the term ''minimum wage'' is used in this chapter, except when such wage is paid to a child seventeen years of age or under, or to a parent, spouse, child or other member of the employer's immediate family. The cost of board, lodging or other facilities shall not be included as a part of the wage paid to any employee to the extent it is excluded therefrom; provided, however, that the commissioner may determine the fair value of such board, lodging or other facilities for defined classes of employees and in defined areas, based on average cost to the employer or to groups of employers similarly situated, or average value to groups of employees, or other appropriate measures of fair value. Such evaluations, where applicable and pertinent, shall be used in lieu of actual measure of cost in determining the wage paid to any employee.