If the director or a classified employee of the Alabama Film Office has previously served as an independent contractor of the Alabama Film Office, and desires to purchase prior service credit for time in the Employees' Retirement System after becoming an active and contributing member of the retirement system under this chapter, he or she shall pay to the Secretary-Treasurer of the Retirement System in a lump sum within five years from August 9, 1995, the full cost of the employer and employee contributions necessary to purchase the prior service credit as determined by the actuary for the retirement system based on the current compensation or final average compensation of the employee, whichever is greater.