For the 1990-1991 school year, the Commonwealth shall pay to each school district which has a market value/income aid ratio of six thousand ten-thousandths (0.6000) or greater and has an actual instruction expenditure per weighted average daily membership for the school year prior to the reimbursable year, which is less than the Statewide median actual instruction expenditure per weighted average daily membership for that year, an amount equal to one and three-tenths percent (1.3%) of the school district's actual instruction expenditure for the reimbursable year: Provided, That no school district shall receive a dollar amount, which, when combined with its actual instruction expenditure for the year prior to the reimbursable year, would result in the district's actual instruction expenditure per weighted average daily membership exceeding the Statewide median actual instruction expenditure per weighted average daily membership for the year prior to reimbursement.