That's the problem with Chinese New Year! Open-season on everyone to charge what they like
I usually try to escape from China during CNY and this time I shot off to Vietnam for 2 weeks of sun
I bought my return airfare ticket from Shanghai to Ho Chi Minh a few months ago and paid RMB1600 in total
By the time the Chinese New Year arrived, that SAME TICKET had a price tag of RMB7260 plus tax (that's FOUR times more than I paid)

The short answer is if you don't want to be ripped-off by taxi drivers, then try not to travel during CNY or take buses and trains instead. If it can't be helped then it's just one more thing in China that we have to live with I guess