Stop Unfair Bid Shopping Act of 2018 or the SUBS Act This bill requires an executive agency awarding a construction contract using sealed bid procedures in an amount greater than $1.5 million to: (1) require an offeror for the contract to include a list in the offer of each subcontractor that the offeror intends to use, for any subcontract expected to be awarded in excess of $100,000; and (2) include a clause in the contract requiring that the prime contractor submit to the agency a written notification of any subcontractor substituted after the award of the contract for a subcontractor so listed, along with an updated estimate for the cost of performing the work associated with the substituted subcontractor.