As I know, the taxi fee from Shenzhen Airport to downtown Guangzhou is no less than 300RMB. Actually, I think you should go to Guangzhou by train. When you arrive at Shenzhen Airport, you could take the airport bus 330 to reach Shenzhen Railway Station in 50 minutes. Then, please catch an inter-city train here to reach Guangzhou in 70 minutes. After arrive in Guangzhou Railway Station, you could catch the metro to Jinzhou quickly., The total fare is about 100RMB per person.