Vayama sent me another email saying that my NH-stock ticket was cancelled by Korean Air. I did have one segment on KE.
FWIW, the usual measure of damages is not what one might have spent in reliance on an expectation of performance but the difference between what one paid (or agreed to pay) under the breached contract and the market price of replacement goods/services. If you have a forward contract for a bag of peanuts and the farmer fails to deliver, the damages are the difference between the contract price and the market price at the time of agreed-upon delivery.
That assumes you're entitled to damages. Unilateral mistake is a defense to breach, provided the non-mistaken party knew or should have known of the mistaken party's mistake. The question is whether this was a mistake. Factually, it doesn't look like one to me. It was failure to monitor currency flutuations. That's carelessness by the party setting the prices, not a mistake.
Of course, this is not legal advice to anyone who might be reading. I am simply stating my position as to my own circumstances.