frist trip to vietnam, coming from China

Hi everyone,

new member here, hoping to find lots of good info on these forums.

I'm planning a trip to vietnam in late april-early may. My gf and I want to go for about three weeks.

I'm having some trouble finding information about flights to and from China. I live in Shanghai and would love to fly directly to Hanoi or Ho Chi Minh, but I would also be happy flying to/from Kunming. If the train is a better idea, I'm also game to try that.

Anyone with experience, who's made a similar voyage, I'd love to hear your advice!

Also, as it is my first time to Vietnam, I really don't know about the cost of things. What budget would be appropriate for three weeks, staying mostly in hostels, doing a moderate amount of shopping, eating a lot, and spending a few nights in a mid-range hotel?

Thanks in advance

R