Subject to rules adopted by the public employees retirement system under section 145.09 of the Revised Code, a contributor participating in the PERS defined benefit plan or contributing under section 145.38 or 145.383 of the Revised Code may deposit additional amounts in the employees’ savings fund established under section 145.23 of the Revised Code. The additional deposits may be made either directly to the retirement system or by payroll deduction under section 145.294 of the Revised Code. The contributor shall receive in return either an annuity, as provided in section 145.64 of the Revised Code, having a reserve equal to the amount deposited or a refund under section 145.63 of the Revised Code of the amount deposited, together with earnings on the amount deposited as the public employees retirement board determines appropriate. If the annuity under the plan of payment selected by the contributor under section 145.64 of the Revised Code would be less than fifty dollars per month, the contributor shall receive the refund.