As per Section-194C If any person making any payment for the works contract then the TDS needs to be deducted only if the amount of payment exceeds Rs.30,000/-. Therefore the limit of Rs.30,000/- is not for the purpose to determine the taxable amount rather it is to determine the applicability of Sec-194C.
Therefore if the payment or the bill amount exceeds Rs.30,000/-, the person became liable to deduct TDS. However TDS is required to be deducted on the whole amount paid or payable for the works contract i.e. in your case on Rs.31,000/-.