Holiday plane tickets, outrageous!

wow, plane tickets for the holidays are super expensive! My sister and her husband are flying home for a week during Christmas. They bought her ticket first (online) and it was $500 (yipes!) but when they went to buy his the price had already doubled to $1000. As a result they are having to take different flights to get here... they are not afraid to fly, but for me that would be terrible! I cannot imagine flying seperately from my husband... I need his support during the flights! By taking different flights they saved a bout $500 on his ticket... but really, that's outrageous!