As I know the hotel has regular shuttle bus heading for HK airport. You'd better go by bus. It is not easy to find a taxi at Guangzhou to Hong Kong, most of the cab should enter Hong Kong, that means you should change another one after you pass the border. It costs 500RMB (about 74USD)from Guangzhou Railway Station to Futian (not the border area but city center), Shenzhen. At the boder, you should take at least 400HKD to HK airport, I guess.