A health care cost management marketplace brings together health care payers and health care cost management vendors. The health care cost management vendors bid on lots of single-claims or multiple claims. Health care cost reduction contracts are awarded to vendors whose bids project the greatest net health care cost reduction savings. Auctions are timed and vendors may change their bids while time remains. Bids include a vendor fee percentage, and, for single claim lots, may further include an estimated cost savings amount. For the single-claim lots, vendors which fail to achieve actual cost reduction savings above a predetermined threshold compared to estimated savings can be penalized.