(a) Unless otherwise provided by law, the county treasurer shall be allowed a commission of two percent (2%) on all school funds paid into his or her hands, except on borrowed money, or the proceeds of the sale of bonds and all other funds on which the law shall not allow commission. In the case of a school district that is composed of area in two (2) or more counties, only the county treasurer of the county in which the school district is administered shall be allowed a commission on the funds of the school district unless the school district has a district treasurer, in which case the county treasurer collecting the school district funds shall be allowed a commission on the funds of that school district.
(b) The county school funds shall pay such proportional part of the salaries and expenses of the county treasurer's office as the total county treasurer's commissions on school funds bear to the total county treasurer's commissions on all funds.