What is the fare in ferry from hk to guangzhou and how to get tax refund after travelling

You mean from HK city proper to Guangzhou or from HKIA?
If you mean from the city proper, in day time, the standard seat costs around 185RMB and the first-class seat costs around 230RMB per adult. For the night vessel, the standard seat costs around 190RMB and the first-class seat costs around 235RMB.

For the taxi, I am not not very clear about it.