Bonds may be sold at either public or private sale. The regents may fix terms and conditions for the sale or other disposition of any authorized issue of bonds. The regents may sell bonds at less than their par or face value, but no bond may be sold at a price below the par or face value of the bond which would result in a sale price yielding to the purchaser an average of more than 12 percent per annum, payable semiannually, according to standard tables of bond values.