I am planning that trip, but in reverse.
The biggest expenses will be shipping your bike, b/c Burma is still closed to vehicles you will need to fly your bike most likely from Nepal to Thailand.
It might be cheaper to have your bike shipped from India to Australia - and buy a 125 or rent a bike in Vietnam, and ride around S.E. Asia on it and sell, and collect your bike in Australia. I know XR250's can be rented in Hanoi for about $80 a day. Thats a lot of days if you factor shipping a bike there will be at least $1k (2 years ago it cost a friend $1600 for a GS).
Rule out China unless you plan on doing some seriously illegal stuff to get in, or spending a lot of money.
Take out upfront costs for however long you want (bike, gear, insurance, shipping, airfares), budget $50 a day for fuel/food/attractions/lodging (even if you are hoping to camp, some areas it may not be enjoyable due to weather/volume of people and getting a hostel/hotel might be less than $10 a night). Obviously it will be more for EU/Aus.
An XR400 would be a good bike to take IMHO - pretty well bullet proof and a lot of the parts cross over with the other Honda models that you will find everywhere. I would personally take something different, but thats mostly coz I am a bit sadistic like that.