Funds for promotional hosting expenditures shall be expended only from gross operating revenues and shall not exceed one percent thereof upon the first two million five hundred thousand dollars of such gross operating revenues, one-half of one percent upon the next two million five hundred thousand dollars of such gross operating revenues, and one-fourth of one percent on the excess over five million dollars of such operating revenues: PROVIDED, HOWEVER, That in no case shall these limitations restrict a port district to less than twenty-five hundred dollars per year from any funds available to the port.