Tourist Visa in HCM before Tet?

Hi. I am Swiss Citizen and plan to travel to China in March. I heard that obtaining the Visa in HongKong is more difficult and more expensive than in Vietnam. Due to the Holidays coming up I wonder wheter I can get my entry permit in Ho Chi Minh City? I plan to leave China by Train (to Mongolia) - do I need to buy it beforehand and enclose a copy? Any other tips or requirements for a swiss citizen traveling by himself?
Thank you very much!