If one of the main vendors of resale properties is to be believed (and the market evidence supports this), about 30 - 40% less than the original contract price.
However as a property is only worth what someone is prepared to pay for it, you also have to consider the fact that the resale market for Corvera may be dead for a considerable time as potential purchasers may well buy properties that have fallen by 30 - 40% on resorts that have been completed.
Mortgage valuations may well come in at reasonable levels but this isn't surprising considering 30% of the contract price has already been paid.
Forget about renegotiating the price.