It takes a night in a train, about 14 hours, costs about 100 Euros as far as I remember...

Dear Mr. Proper,
It is so easy to go to Harbin by train , the ticket is is about 10 to 50 USD , depends on the class and speed, and the fast one will take 6 hours from Beijing to Harbin.
when you arrive in Harbin train station you will find good and cheap hotels not so far from the railway station.

Getting to Harbin is not normally a problem (planes, trains and buses available). However, you have to consider that you are going when 'the world and his wife' will also be going. You should buy your tickets via an agent ( do you know about ticket sales here?)and make sure you have a hotel booked before arrival. Also, it's Chinese New Year in approx.3 weeks (Ox), which means a seething mass of people moving about the country. I'm sure I sound like doom and gloom, but previous messages are misleading. Have fun when you get there. (Should you have to downsize, consider a similar festival at Beiling Park, Shenyang, Liaoning Province.)