For the biennium ending June 30, 1985, the annual increase in the cost per service unit paid to any vendor under medical assistance and general assistance medical care shall not exceed five percent, except that the five percent annual increase limitation applied to vendors under this subdivision does not apply to nursing homes licensed under chapter 144A or boarding care homes licensed under sections 144.50 to 144.56. The estimated acquisition cost of prescription drug ingredients is not subject to the five percent increase limit, any general state payment reduction, or cost limitation described in this section, except as required under federal law or regulation. For vendors enrolled in the general assistance medical care program, the annual increase in cost per service unit allowable during state fiscal year 1984 shall not exceed five percent. The basis for measuring growth shall be the cost per service unit that would have been reimbursable in state fiscal year 1983 if payments had not been ratably reduced and if payments had been based on the 50th percentile of usual and customary billings for medical assistance in 1978. The increase in cost per service unit allowable for vendors in the general assistance medical care program during state fiscal year 1985 shall not exceed five percent. The basis for measuring growth shall be state fiscal year 1984.