Guangzhou to Sanya train ticket online booking

Can I buy Express train (T201/T204) ) ticket from Guangzhou to Sanya on the departure date at Guangzhou Railway Station ?

I am plan to have a visit to Sanya with two kids on 24-27 November. We will be traveling from Shenzhen to Guangzhou on 23rd November and wish to get the train tickets to Sanya on the same day. Is it necessary to buy that tickets in advance from departure date? I was trying very hard to purchase the ticket online, but I only found a website Chinatrainticket selling the Hard seat ticket for USD70, that is very expensive if compare to the price I get from other website ex. Chinatrainguide which is RMB209 for a Hard seat.