So, the loss in value is 950,000 kroner and the "cost avoided" is 700,000 kroner, so R&G are entitled to 250,000 in damages.

If you want to know where these damages came from, 150,000 kroner is the "benefit of the bargain, i.e., the amount attributable to the fact that they negotiated a good deal when they made the contract, and 100,000 is the return of their down payment.