oh man...i was planning that last year too. Lol, my really cheapo way is as below
1.fly airasia to Kl. Take a really cheapo flight from KL to shanghai. Muck around shanghai for 1-2 days
2. take train from shanghai to beijing. Muk around beijing for 1-2 days
and begin the journey proper. It takes a total of 6 nights and day of pure train travelling to travel that few thousands miles. the lonely planet i was reading mention that the REAL joy of this railway is to well sit and watch and maybe have a cup of coffee...the scenary/cultural/reglion changes.
You can choose to go pass monglia or the russia hinterland.
They recommend a few stops along the way like lake Bahkral and a couple of towns. Takes about 10 days.
You will end up in Moscow, which isn't really interesting...So pple recommend going down to St Pte.
From St Pte...and here's the part i didn't figure out to do cheaply, to get to london...And from london, airasia cheaply back to KL...