quickest and cheapest way to get from Shenzhen Airport to Guangzhou please. After 9pm

You can take subway line 11 to Qianhaiwan to transfer to line 1, and then transfer to line 5 at Bao’an Center. Get off at SZ North Railway Station to catch the bullet train to Guangzhou. It takes about 40mins and CNY74.5 for a second class seat, CNY99.5 for a first one by the train.