The administrative expenses of the board of trustees, including all operational expenses, fees, compensation, and other costs, shall be paid from funds held by it and may be chargeable by it to either principal or income or both, as determined by it, as of any valuation date. Further, the board of trustees shall have the authority to allocate expenses among member municipalities on the basis of costs. Administrative expenses for the first year of operation may be assessed against first year contributions in proportion to the number of participating employees.