Here is some advice for travelling on the Trans-Siberian from Beijing to Moscow.
Option 1: Buy tickets in person at Beijing...
The absolute cheapest way to buy westbound Trans-Sib tickets is in person at one of the reservation offices in Beijing. However, the two weekly Beijing-Moscow trains get booked up well in advance, so buy tickets as far in advance as you can. Westbound trains are easier to get berths on than eastbound trains, and winter is easier than finding a place than the peak summer season from May to September. Train 3 to Moscow via Mongolia is often fully booked a couple of weeks in advance especially in summer, although it can be easier to get a berth on train 19 via Manchuria, which occasionally has berths available even a few days before departure (but not always!). The basic message is this: If you positively have to be on a specific train on a specific date, forget booking at the ticket office, you should pre-book via CITS or some other agency and pay their extra fee. But if you're living in Beijing, or plan to be there for some time before leaving, and can be a bit flexible about exactly what date you leave, booking in person can be a good option. You can buy Trans-Siberian train tickets in person in Beijing at:
the international train booking office on the ground floor of the Beijing International Hotel. This is about five minutes walk north of Beijing main station on Jianguo Men Nei Dajie, open 08:30-12:00 & 13:30-17:00 Monday-Friday, 09:00-11:00 & 14:00-16:00 on weekends and holidays. The staff speak basic English and leaflets are available with international train times in English.
Beijing main station (metro Bejingzhan), in the ticketing office for foreigners. This is on the north west corner of the 1st floor, accessed via the soft seat waiting room, open 05:30-07:30, 08:00-18:30, 19:00-23:00. It's now reported (2008) that this office no longer sells international tickets.
BTG Travel & Tours, on Fwai Dajie between the New Otani and Gloria Plaza Hotels, open 08:00-20:00. They have a desk for Trans-Siberian tickets, with information in English.
Option 2: Buy tickets by phone or email with China Travel Service (CITS)...
CITS are the official Chinese state tourist agency, and this is probably the cheapest way to buy westbound Trans-Sib tickets starting in Beijing, other than buying in person at the ticket office. You can book trains from Beijing to Moscow, Irkutsk or Ulan Bator by emailing support-en@cits.com.cn (you can check details on the CITS website, www.cits.net) or by calling CITS on + 86 10 6512 0507 or + 86 10 6512 0503). It was reported back in 2005 that CITS had stopped taking email or phone bookings, but they are now taking bookings by email again. Expect to pay by bank transfer rather than credit card. Reports also suggest they can't book Beijing-Irkutsk tickets, only Beijing-Krasnoyarsk and beyond, so by all means ask for Beijing-Irkutsk, but be prepared to accept an offer of a Beijing-Krasnoyarsk ticket and simply get off in Irkutsk (though their website shows Beijing-Irkutsk fares!). They will still be the cheapest way to buy tickets!
Option 3: Buy tickets through an agency in China or Hong Kong...
If you're in China or Japan and want an agency to arrange your westbound Trans-Siberian trip, try one of these two agencies:
Monkey Shrine (www.monkeyshrine.com). Monkey Shrine is an experienced China-based tour agency who can arrange a tailor-made itinerary with stop-overs and hotels along the way, plus help with visas. Monkeyshrine offer a good service, but are naturally more expensive than booking it all yourself via CITS. A key advantage is being able to arrange onward tickets, not just tickets starting in Beijing, and to arrange hotels or tours along the way.
Chinatripadvisor (www.chinatripadvisor.com): If you just want the Trans-Siberian train ticket, a cheaper option is to buy it through www.chinatripadvisor.com. Beijing to Moscow costs $585 in 2nd class 4-berth or $939 in 1st class 2-berth on Trans-Mongolian train 3, or $659 2nd class, $999 1st class on Trans-Manchurian train 19.
If you want more detailed information check the site where I got this info from at:
Trans-Sib.