65 ILCS 5/9-2-100
Except as otherwise provided in Section 9-2-113, any work or other public improvement, to be paid for in whole or in part by special assessment or special taxation, when the expense thereof will exceed $10,000 , shall be constructed by contract let to the lowest responsible bidder in the manner prescribed in this Division 2. Such contracts shall be approved by the president of the board of local improvements.
In case of any work which it is estimated will not cost more than $10,000 , if after receiving bids it appears to the board of local improvements that the work can be performed better and cheaper by the municipality, the corporate authorities of the municipality shall perform that work and employ the necessary help therefor. The cost of that work by the municipality in no case shall be more than the lowest bid received.
65 ILCS 5/9-2-100