What does it cost and why?

The Federal Acquisition Regulations (FAR) 52.203.5 expressly prohibits any company from receiving compensation based upon GSA acting favorably towards a prospective vendor. Therefore, it is illegal for MarketUS to accept a commission against your potential GSA sales. An officer of your company may have to sign a Standard Form 119 certifying that you are not/will not pay a contingent fee resulting from this contract. Sorry!