Which is the fastest and cheapest way to reach hongkong international airport from guangzhou

First of all, I wanna inform you that you cannot get a way that is fastest and cheapeast.
Here are the ways for your reference:
Fast: at 09:30 on Thursday and Saturday, a ferry leaves from Nansha Port to HKIA. It takes around 80min and the fare is 265RMB for an economy class cabin and 350RMB for the VIP cabin.

Economy: Go to Guangzhou Dong Shan Hotel, Yuxiu Nan Coach Terminal, Hotel Landmark Canton or Garden Hotel to take a direct cross-border bus to HKIA. It takes 3.5-4h and the fare is 250HKD.